Sleep begins in utero (Payne & Bach, 1965; Petre-Quadens, De Barsy, Devos, & Sfaello, 1967). Electrical discharges can be recorded from the fetal brain during sleep from about 3 months gestation, and mature and consolidate by 4 months postpartum as two distinct sleep rhythms (Mirmiran, Maas, & Ariagno, 2003). These rhythms are known as Rapid Eye Movement (REM) and nonRapid Eye Movement (NREM) sleep rhythms. These two rhythms are physiologically distinct from each other and cyclically alternate during the night in what is known as the ultradian rhythm. Differences between the two rhythms are outlined in Table 2.1.

During NREM sleep, the normal regulatory systems of the body continue to function, and body movement is preserved (Mindell & Owens, 2003). NREM is categorized into four distinct stages which represent gradations in depth of sleep and difficulty of arousal. The way NREM sleep cycles through the stages is shown in Fig. 2.1. At the beginning of the night, the sleep cycle enters into stage one NREM sleep. Stage one is considered a transitional phase between sleep and wakefulness. The child can easily be woken when in this stage and it constitutes about 2%–5% of total sleep. The majority of this sleep stage occurs at the start of the night as the cycle often bypasses this stage during the sleep cycle during the night (Adair & Bauchner, 1993). Stage two is considered the onset of sleep. There are decreased eye movements, reduced muscle tone, and reductions in respiratory rate and heart rate. In childhood, about half of the total sleep time is spent in stage two which predominantly occurs in the middle of the night (Adair & Bauchner, 1993). The third and fourth stages are almost identical in nature albeit stage four is the deepest sleep stage. They are often called slow-wave sleep (Mindell & Owens, 2003). The child will have a relaxed body, slow and rhythmic breathing, and a decreased heart rate. This stage is the hardest to wake a child from, and, if awoken, they may appear confused and disorientated. These two stages appear predominantly in the early period of sleep and constitute about 20% of total sleep time (Adair & Bauchner, 1993). NREM ends when REM sleep commences.

REM sleep is characterized by absent muscle tone, high levels of cortical activity, and bursts of phasic eye movements under closed eyelids as well as irregular heart and respiratory rates (Mindell & Owens, 2003). It is thought to be the time for the brain to assimilate images by replaying them during dreams and to enable the child to learn from the experiences of the day (Adair & Bauchner, 1993). The child’s muscles are generally paralyzed during this period which is thought to prevent a child from acting out their dreams. The proportion of REM sleep is highest in infancy and declines throughout childhood (Garcia-Rill, Charlesworth, Heister, Ye, & Hayar, 2008). A short period of REM sleep may follow after which the child descends back into the four NREM sleep stages before passing into REM sleep again. This episode of REM sleep ends when the child enters stage two NREM sleep. If the child enters stage one NREM, then brief arousal may occur.

During a typical night of sleep, individuals cycle through the REM and NREM stages, often referred to as the ultradian rhythm. In infants, these cycles last up to 50 minutes, increasing to about 1.5 hours in adults. At the end of each cycle, it is common to experience a brief arousal followed by a rapid return to sleep. Therefore children may briefly wake up to 5–7 times a night. The proportion of REM and NREM changes throughout the night. At the start of the night, individuals spend longer in NREM sleep (first third of the night), with the proportion decreasing with each cycle to the point in which individuals spend longer in REM sleep (last third of the night). The duration and timing of each sleep stage is influenced by a number of factors. Individuals who have experienced sleep disruptions will have a higher proportion of slow-wave (i.e., deep sleep) during subsequent recovery sleep.

Sleep patterns change and develop from infancy to adulthood. Newborn babies exhibit an even distribution of about 8 h in each of REM and NREM sleep (Roffwarg, Muzio, & Dement, 1996). From birth, there is a gradual decrease in REM sleep to just 1 hour in adults, whilst NREM sleep decreases to about 6–7 hours per day in adults (Coons & Guilleminault, 1982; Roffwarg et al., 1996). At 6 months, REM sleep is predominantly at night, and daytime naps cease around age four. The increase in waking hours over time is predominantly at the expense of REM sleep duration (Garcia-Rill et al., 2008). By the time infants have reached their second 6 months of life, they should have passed through a series of developmental and physiological milestones which enable them to initiate and maintain sleep through the night (Coons & Guilleminault, 1982). In contrast to infants, who spend majority of their time sleeping throughout the day with multiple night-time awakenings, sleep begins to consolidate into one to two naps by 1 year of age, to one nap in the toddler period to eventually all night-time sleep by the time children are aged four (Iglowstein, Jenni, Molinari, & Largo, 2003). As children reduce their naps, their overnight sleep should become consolidated with fewer nocturnal awakenings (Iglowstein et al., 2003; McLaughlin Crabtree & Williams, 2009). Despite this, however, over one-fifth of Australian primary caregivers report their child has problems with night wakings in their preschool years (Hiscock et al., 2007; Quach, Hiscock, Canterford, & Wake, 2009).

Sleep and wakefulness are regulated by two coupled processes, known as the “two process” sleep system, as proposed by Alexander Borbely from studies in rats (Borbely, 1982; Borbély, Daan, Wirz-Justice, & Deboer, 2016). The two processes are:

Circadian rhythm refers to the natural biological cycles that attune individuals to day and night. Consolidated overnight sleep is thought to occur as the result of an increase in circadian sleep drive during the night that opposes the decline in homeostatic sleep drive during sleep (Dijk & Czeisler, 1995; Edgar, Dement, & Fuller, 1993).

The circadian rhythm is a predictive rather than reactive process regulated by the suprachiasmatic nucleus of the hypothalamus (Mistlberger, 2005). Prior to waking, body temperature, sympathetic autonomic tone, and plasma cortisol levels rise, possibly anticipating the body’s increased energy demands associated with wakefulness. The rhythm is characterized by periods of maximum sleepiness (circadian troughs) and maximum wakefulness (circadian nadirs). There are two periods of maximum sleepiness, one being in the late afternoon and one in the middle of the night, and two periods of maximum wakefulness, one in the early morning and one in the evening. Although these circadian patterns exist, the level of wakefulness and alertness is influenced by other factors such as individual variation, nature of tasks, and environmental factors. For example, high energy activities (e.g., playing sport, running) before bedtime can increase wakefulness which makes going to sleep harder.

In addition, the circadian rhythm is synchronized to environmental cues, otherwise known as zeitgebers. The most powerful of these zeitgebers is the light–dark cycle (Fisk et al., 2018). The light–dark cycle is regulated by the release of an endogenous substance known as melatonin from the pineal gland (Wetterberg, 1999). In a dark environment, melatonin is released to activate the sleep pathway in the brain. In a light environment, melatonin release is inhibited (Zisapel, 2018). The light–dark cycle can affect the sleep–wake cycle since light can be a cue for decreased sleep drive. However, the process can be overridden if the person’s sleep drive is strong enough. The circadian rhythm is also influenced by other time cues such as the timing of meals, alarm clocks, and other scheduled activities, for example, going to school.

Therefore, the activation and regulation of sleep is controlled by environmental and internal cues. The synchronization of environmental and internal cues to the circadian rhythm highlights the importance of regulated daytime schedules and sleep environment. For example, having inconsistent time cues due to variable wake times or meal times can disrupt the circadian rhythm. Likewise, having an inappropriate sleep environment which contains light from a TV set may inhibit the release of melatonin which is crucial for the initiation of sleep.

The homeostatic component is the sleep drive which intensifies whilst a person is awake, and declines whilst a person is sleeping (Beersma & Gordijn, 2007; Fuller, Gooley, & Saper, 2006). Homeostatic regulation of sleep works in a similar way to the hunger homeostatic process. Your hunger drive increases the longer it has been since you have consumed food and also depends on the amount of food you last consumed. Similarly, your sleep drive increases the longer you stay awake, and can also be influenced by the quality and quantity of the last sleep you last had.

Understanding the role of sleep–wake regulation and sleep architecture provides the basic knowledge to explain the etiology for many sleep problems experienced by children. For example, night wakings are more common in infants and toddlers as prolongations of the normal night-time arousals that occur at the end of each sleep cycle. The partial arousal parasomnias, such as sleep walking and sleep terrors, usually occur in the first third of the night because that is when deep sleep is the most dominant. These sleep problems are also prevalent in children who experience conditions which increase the likelihood of rebound sleep, such as sleep deprivation or withdrawal of medications. On the other hand, nightmares are associated with light sleep due to the high cortical activity. Obstructive sleep apnea (OSA) is common in REM sleep, where the normal REM changes in breathing regulation compound upper airway collapse in at risk children (Horne et al., 2011).

Sleep duration is an important indicator of sleep need and varies between different age groups and also between individuals (Acebo et al., 2005; Galland et al., 2012; Iglowstein et al., 2003; Price et al., 2013; Sadeh, 2007; Spilsbury et al., 2004; Williams, Zimmerman, & Bell, 2013). However, few studies have examined the differences between age and individuals in a large longitudinal cohort.

Although there are recognized national guidelines, such as the American Academy of Sleep and Australian Sleep Health Foundation, there is substantial individual variation in a person’s sleep needs and their tolerance for sleep loss (Hirshkowitz et al., 2015). Parents are good at recognizing when a child is tired in association with an acute sleep loss like a missed nap or late bedtime but do not always associate these daytime symptoms with chronic sleep loss. Total sleep duration is highest in infancy, with an average of 14.0 h (SD=2.2 h) for infants under 6 months spread over about six sleep episodes. This total duration decreases to about 10 hours (SD=2 h) by the time children are 9 years of age, with further decreases to about 8 hours by adolescence (Price et al., 2013). In addition to changes in sleep duration, consolidation of night-time sleep occurs during the first year of life, with a decreasing trend of daytime sleep as children have fewer naps. Typically, regular daytime naps disappear by the age of 4 years, with any naps being of <30 minutes past this age.

Longitudinal studies in different countries have affirmed similar development of sleep duration patterns, signifying the underlying biological regulation of sleep need (Iglowstein et al., 2003; Price et al., 2013; Williams et al., 2013). A child’s sleep duration tends to track over time. Children who sleep only short periods compared to their contemporaries in early childhood also do so during later childhood (Jenni, Molinari, Caflisch, & Largo, 2007; Russo, Bruni, Lucidi, Ferri, & Violani, 2007). This is also true for long sleepers. In addition, some children may naturally stay awake later and rise later (commonly known as owls), whilst other children may go to bed earlier and rise early the next morning (commonly known as larks) (Blader, Koplewicz, Abikoff, & Foley, 1997). The research indicates that an important indicator of good sleep is that a child’s intrinsic sleep requirements are fulfilled rather than a child achieves a set amount of sleep per 24 h per se.

For many children, the first instance they are required to be awake by a required time may be when they attend preschool or commence school or their parents go back to work. This may be particularly problematic for children who are natural night “owls,” as they are woken before their intrinsic sleep requirements are achieved after going to sleep later than their “lark” peers. Children who have a further distance to commute may have to wake up earlier than their peers and thus also experience shorter sleep durations (Adam, Snell, & Pendry, 2007). The reduced sleep durations during the week may lead some children to sleep in later on weekends (Touchette, Mongrain, Petit, Tremblay, & Montplaisir, 2008). A reduction in as little as 30 minutes of sleep from a child’s normal sleep duration can impact on the child’s daytime functioning through decreased attention, memory retention, and increased behavioral difficulties (Sadeh et al., 2003; Suratt et al., 2007). However, research has also highlighted that there are not specific thresholds of optimal sleep for child outcomes, highlighting the individual variation in a person’s intrinsic sleep need (Price, Quach, Wake, Bittman, & Hiscock, 2016). Therefore, children need to have an adequate bedtime which allows for an appropriate amount of sleep to be achieved before they need to wake up to prepare for school.

Sleep hygiene refers to a list of behavioral and environmental conditions and other sleep-related factors connected to effective and efficient sleep (Spilsbury et al., 2005; Stepanski & Wyatt, 2003). The importance of sleep hygiene was first reported for adults (Hauri, 1992) and then children (Blum & Carey, 1996; Owens & Witmans, 2004). Poor sleep hygiene exists when a child has variable sleep and wake-up times, poor sleep-related behaviors, or a poor sleep environment. Behavioral sleep interventions must target these components in order to develop and/or maintain positive sleep hygiene practices (see Chapter 5). Development of appropriate sleep hygiene may set the foundation for the development of long-lasting positive sleep behaviors as children become adolescents and adults (Mindell & Meltzer, 2008; Owens & Witmans, 2004).

Good sleep hygiene practices are considered to include: having a set bedtime routine which is consistent for all nights of the week, avoiding caffeine or high sugar consumption in the afternoon, avoiding excessive media exposure (>2 hours per day), avoiding television and game system use before bed and making the period before bedtime relaxing (Mindell, Meltzer, Carskadon, & Chervin, 2009; Owens & Witmans, 2004; Uebergang, Arnup, Hiscock, Care, & Quach, 2017).

Children with poor sleep hygiene practices are more likely to have a sleep problem. A study of 4243 US adolescents reported caffeine consumption was associated with a 1.9 times increased likelihood of difficulty sleeping and 1.8 times increased likelihood of morning tiredness due to later bedtime (Orbeta, Overpeck, Ramcharran, Kogan, & Ledsky, 2006). Similar figures have been reported in Australian children in the first year of primary school, with approximately 30% reporting having a high sugar or caffeinated drink after school (Quach, Hiscock, & Wake, 2012).

The importance of a consistent nightly bedtime routine has been highlighted in a randomized controlled study involving 206 infants (aged 7–18 months) and 199 toddlers (aged 18–36 months). By establishing a consistent nightly bedtime routine, intervention mothers reported improved infant and toddler sleep and an improvement in their own mood (Mindell, Telofski, Wiegand, & Kurtz, 2009). Another study of 135 Japanese children aged 4–6 years reported that irregular bedtimes were associated with increased behavioral problems in a community sample (Yokomaku et al., 2008). Whilst a recent study, in 4901 Australian children starting primary school (aged 5–6 years), found that inconsistent bedtimes on both school and nonschool nights were associated with a twofold increase in the likelihood of the child having a sleep problem, once considering other factors such as media use at bedtime, gender, and socioeconomic status (SES; Uebergang et al., 2017). This suggests that a consistent bedtime and bedtime routine are critical for achieving and establishing good sleep patterns and should be the foundation of any behavioral sleep intervention. However, the relationship between consistent bedtimes and sleep problems remains to be explored in children once they have commenced school.

Televisions have existed in homes for many decades and are widely watched by children (Bernard-Bonnin, Gilbert, Rousseau, Masson, & Maheux, 1991). The impact of media use on sleep problems was first described in a study of parents of 495 students from kindergarten to fourth grade in the United States (Owens et al., 1999). The authors reported that, although parents closely monitor their child’s TV viewing habits, almost a quarter of children had a television in their bedroom. Children who watched more TV during the day and around bedtime had more problems with bedtime resistance, sleep-onset delay, anxiety around sleep, and shortened sleep duration. A study of 321 US children aged 5–6 years reported that children who are exposed to television, either watching actively or passively in the same room, are at greater risk of having sleep problems such as going to bed (Paavonen, Pennonen, Roine, Valkonen, & Lahikainen, 2006). In particular, children who are passively exposed to television are almost three times more likely to have sleep disturbances. In 19,299 Chinese children, those who watched more than 2 hours of television per day were 1.63 times more likely to have bedtime resistance problems and 1.37 times more likely to have poor sleep duration (Li et al., 2007). Another study of 1473 caregivers reported that for children aged over 3 years, simply having a TV in the child’s bedroom is associated with a reduced sleep duration (Mindell et al., 2009). Similar findings have also been reported in other studies and have been extended to other media such as computer and game system use in school-aged children (Dworak, Schierl, Bruns, & Struder, 2007; Gaina et al., 2007; Kuriyan, Bhat, Thomas, Vaz, & Kurpad, 2007; Mistry, Minkovitz, Strobino, & Borzekowski, 2007). The appropriate daily use of television, particularly around bedtime, may be important in reducing child sleep problems. Current guidelines in Australia and America recommend limiting media use to a maximum of 1 hour per day for children between 2 and 5 years, with no screen time in the hour before bed (Cain & Gradisar, 2010; Council on Communications and Media, 2016). Although the same recommendations do not suggest a maximum amount of screen time for children aged 5–18 years, it also highlights that screens (i.e., televisions) should be present in the bedroom as well as not in the hour before bed. These studies suggest that media exposure is strongly associated with increased sleep problems and therefore should be discussed as part of an intervention.

The International Classification of Sleep Disorders (ICSD) was first published in 1990 and has been revised several times with the latest revision published in 2014 (American Academy of Sleep Medicine, 2014). It has gained wide acceptance as an important tool for clinicians and researchers in sleep medicine, as it provides a comparative framework to enable research results to be translated into clinical practice. The classification has attempted to classify disorders according to their clinical significance and expression.

Some of the disorders described in the ICSD, such as limit-setting disorder, are almost exclusively found in children, whereas others, such as insomnia, list diagnostic criteria that are intended to be applied to both adult and pediatric populations. This latter approach may not adequately capture developmental considerations or reflect the most common clinical presentations of these disorders when they occur in preschool and school-aged children (Mason & Pack, 2007; Mindell & Owens, 2003; Robinson & Waters, 2008). In addition, the stringent classification criteria do not acknowledge the validity of parental concerns and opinions regarding their child’s sleep patterns and behaviors. The perception of a child sleep problem may be a potential trigger for seeking help from healthcare providers. One study of 154,957 patients aged 0–18 years reported that 3.7% of children meet ICSD criteria for a sleep problem (Meltzer, Johnson, Crosette, Ramos, & Mindell, 2010). This is substantially lower than prevalence rates reported by objective (i.e., actigraphy) and subjective (i.e., parent report) measures in epidemiological studies, which suggests that the exclusive use of the ICSD may result in underdiagnosis of sleep problems in children (Hiscock et al., 2007; Lazaratou, Dikeos, Anagnostopoulos, Sbokou, & Soldatos, 2005; Owens, Spirito, et al., 2000).

Parasomnias are disorders in maintaining sleep and are often a consequence of genetic disposition combined with disassociation between wakefulness, NREM sleep and REM sleep (Kotagal, 2008; Mahowald & Schenck, 1992). They occur predominantly during sleep but also during the transition period between sleep and wake states. They are often broadly grouped as either (1) arousal disorder (sleep terror), (2) parasomnias associated with REM sleep (nightmares), (3) sleep–wake transition (rhythmic movement disorder), and (4) parasomnias associated with any sleep stage. Although parasomnias are considered a benign phenomenon (i.e., they do not usually have a serious impact on sleep quality and quantity), they can result in injury to the child and be disturbing for either the child or the family (Petit, Touchette, Tremblay, Boivin, & Montplaisir, 2007).

Cultural norms are another important factor in distinguishing the boundary between “normal” and “problematic” sleep in the family context. It is unreasonable to assume that all families have the same beliefs and expectations when it comes to children’s sleep. What defines a sleep problem is highly dependent upon a family and their cultural background. The when, how long, with whom and where of “normal” sleep is not easily defined, as research has highlighted that numerous aspects of sleep are influenced by cultural standards (Jenni & Werner, 2011; Mindell, Sadeh, Kwon, & Goh, 2013; Palmstierna, Sepa, & Ludvigsson, 2008). Common disparities in child sleep expectations have centered around sleep needs and duration, bedtime routine, and sleeping arrangements (Milan, Snow, & Belay, 2007).

Sleep duration and sleep need are the main focus of most studies involving children’s sleep. Children in Italy between the ages of two and four have been reported to have shorter sleep durations then children in other countries because they often participate in evening social activities with adults (Ottaviano, Giannotti, Cortesi, Bruni, & Ottaviano, 1996). Chinese and Japanese school children have shorter sleep times due to later bedtimes and early rise times associated with a societal focus on academic success (Liu, Liu, & Wang, 2003; Steger, 2003). However, one study comparing sleep patterns and durations between elementary-aged children in the United States (n=494, 5–11 years old) and China (n=517, 7–13 years) reported that the differences in sleep duration between the two cultures, 1 hour less in Chinese students, was associated with more sleep problems and increased daytime tiredness (Liu et al., 2005). The authors did not measure whether there were differences in caregiver perception of a child sleep problem as their measure was originally validated in US children and reflected common practices in that country. The result from this study suggests that the amount of sleep a child needs does not necessarily differ amongst cultures, even though expectations may.

Another common difference is the importance of a set bedtime routine. Most western countries tend to have a high focus on having a distinct presleep routine (Beltramini & Hertzig, 1983). The routine often commences after dinner and involves events such as a bath, dressing in sleep clothes, telling stories, and the child sleeping in their own bed, in their own room, at a set bedtime. By contrast, other countries such as Italy, Spain, and Greece have an unstructured and flexible bedtime (Jenni & O’Connor, 2005; Ottaviano et al., 1996). Although the benefits of having a set bedtime routine have been demonstrated (Mindell et al., 2009), caregivers who do not have an expectation of a consistent bedtime routine and sleep hours may define sleep problems differently than those who do have expectations in these areas. One study of 510 preschool children (age 2–5 years) compared sleep schedules in white, black, and Hispanic families over a 24-hour-period in the United States (Lavigne et al., 1999). Children from the three different cultures had the same amount of sleep. However, the distribution of sleep differed, with more black and Hispanic children reported to have an afternoon nap. Although this may be acceptable during the preschool years, it would impact on child sleep duration at school entry as naps at school are generally not accepted in many Western countries.

The practice of cosleeping refers to when parents share the same bed as their children. This practice has been widely studied with the predominant western conception being that it is not “normal” to cosleep (BaHammam, Alameri, & Hersi, 2008; Berkowitz, 2004; Claudill & Plath, 1966; Cortesi, Giannotti, Sebastiani, & Vagnoni, 2004; Cortesi, Giannotti, Sebastiani, Vagnoni, & Marioni, 2008; Jenni, Fuhrer, Iglowstein, Molinari, & Largo, 2005; Latz, Wolf, & Lozoff, 1999; Liu et al., 2003; Mao, Burnham, Goodlin-Jones, Gaylor, & Anders, 2004; McKenna, Ball, & Gettler, 2007; Shweder, Jensen, & Goldstein, 1995; Weimer et al., 2002; Worthman & Brown, 2007). However, research has shown that it is more often the norm than not. The practice is not isolated to less industrialized countries but is common in technologically advanced countries such as Japan (Latz et al., 1999; Mao et al., 2004).

Many of these cultural beliefs have been influenced by climatic factors, family size, availability of space, and the beliefs about individual independence or family interdependence (Stearns & Rowland, 1996). Therefore, a vast difference in sleep beliefs and expectations exists between cultures and informs the notion of normal sleep for particular families. It is important to take parental perception into account when offering an intervention program. Parents who identify a sleep problem may be more likely to seek assistance and follow through with interventions to improve their child’s sleep than parents who do not.

Sleep problems are associated with poor parent mental health in the preschool years (Bayer et al., 2007; Hiscock & Wake, 2001; Martin et al., 2007; Parfitt & Ayers, 2014), but it is not known if this is true for school-aged children. Research in chronically ill children suggests an association between child sleep and poor parent mental health (Boman, Lindahl, & Bjork, 2003; Cottrell & Khan, 2005; Jan et al., 2008; Meltzer & Moore, 2008; Moore, David, Murray, Child, & Arkwright, 2006). However, it is unclear whether the sleep problems had a direct association with parent mental health or whether the child’s diagnosis was the predominant factor. In infants, sleep problems increase maternal report of postnatal depression symptoms, and treatment of the infant’s sleep problem results in a significant improvement in maternal mood (Hiscock & Wake, 2001, 2002).

Only a few studies have examined the impact of preschool and school-aged child’s sleep problems and parent mental health in healthy populations.