During the nineteenth century, the first books on infant/child care had been published but sleep in those books was almost completely neglected and was never viewed as a problem. The fact that sleep at night was not consolidated and some activities went on during the night might have led to night awakenings not being considered as disrupting sleep or rest. With the advent of artificial light and the regulation of working and school hours, habits have dramatically changed and sleep has become more and more consolidated into one single bout per night. At the beginning of the twentieth century, the first recommendations for sleep need for infants and children have been published.

The literature of the 1800s includes books by doctors and medical professors that give recommendations about infant sleep and expectations with regard to “normal sleep” (e.g., “newborns don’t sleep for more than 2 hours at a time,” “children won’t sleep through regularly until about 17 months”). Also, in their writings, we can find some useful advice: “by about 6 months of age babies could get used to sleeping at specific times of the day and that mothers should not rush to comfort the baby immediately, but should instead see if it resettles on its own.”

Looking at the first scientific publications that can be accessed through PubMed, we found some interesting papers that could give us a picture of how sleep was considered in the first decades of the past century. In one of these papers, “Sleep Requirements of Children” published in the California State Journal of Medicine in 1921, there were recommendations for the amount of sleep for each age and several statements of common sense that would have been demonstrated scientifically several years later by the literature [8].

In a lecture at the Section of Diseases of Children at the combined meeting of the British and Canadian Medical Associations, published in 1931, Dr. Cameron categorized sleep disturbances as follows: (1) sleeplessness and continuous crying in young infants, (2) sleeplessness in older children, (3) night terrors, and (4) enuresis. Describing sleeplessness in infants, he identified three causative factors: (a) pain (mainly colic or dyspepsia or aerophagy treated with chloral hydrate 10 min before each feed) or discomfort (nasal obstruction treated with few drops of adrenaline solution in the nostrils before the child is put to the breast), (b) inherited or constitutional neuropathy (that resembles the description of neonatal hyperexcitability), and (c) faulty management that resembles the description of behavioral insomnia of childhood [9]. Dr. Cameron affirmed that most infants who are sleepless and who cry constantly without any specific pain or discomfort do so because the management is faulty: “It is through the mother or the nurse that we must work to get our effects….” Dr. Cameron also suggested some practices to help crying infants , such as the primitive habit in all countries of putting the crying infant in the swaddling clothes and enveloped in the steady pressure of a light and porous shawl, or putting the infant up against the mother’s back (as in the African culture), so that he/she takes no part in the expression of her emotions, and divulging her thoughts from the child would lead the restless infant to soundly fall asleep. Interestingly, he finally expounded on a theory by which hypoglycemia or the presence of ketone bodies in the blood leads to enuresis, sleepwalking , and night terrors.

In a paper published in 1936 [10], the causes of disturbances of sleep in children had been classified as: (1) Constitutional neuropathy: This included restless children who did not fall asleep easily and who were easily aroused by even trivial environmental stimuli; this was attributed to a calcium deficiency and treated with calcium. (2) Sleep disturbances accompanying disease: in infants, painful conditions like otitis media, pain of colic and intestinal disturbances, hunger, teething, and eczema; and in older children, renal colic, rheumatic fever, cardiomyopathies, and respiratory difficulties. Preferred treatments were narcotics (codeine very effective) and the barbiturates were given freely, especially when there was considerable restlessness. (3) Faulty physical and mental hygiene: Disturbed sleep or failure to fall asleep may be due to uncomfortable or too much clothing or emotional disturbances. The author suggested that, in infancy, faulty sleeping habits are easily established and difficult to overcome. Overstimulation, as represented by a too-ambitious school program, too many extracurricular activities (dancing, music lessons, etc.), premature and untimely participation in social affairs and pleasures of the adult, and unsuitable movies and radio programs, are not conducive to restful sleep. (4) Temperatures on the child: The high temperature would determine a tremendous increase of the child’s motor activity. (5) Heavy meals: A heavy meal at night is prone to cause not only excessive motor activity but also terrifying dreams, crying out in sleep, and a constant turning in bed.

The famous pediatrician Benjamin Spock, in the late 1940s, made recommendations that have been greatly influential throughout the next several decades. The advice for getting the baby to sleep was: “The cure is simple: Put the baby to bed at a reasonable hour. Say good night affectionately but firmly, walk out of the room, and don’t go back…” [11].

In a following paper in Pediatrics (1949) [12], Spock stated that chronic resistance to sleep in infancy is a behavior problem which was formerly rare but was becoming more frequent, and its frequency seems to be related to the trend toward self-regulation to babies and to confusion in how to apply this philosophy . The treatment of sleep problem in the baby less than one year of age with the crying-out method showed that most of these babies would cry indignantly from 10 to 20 min the first night and perhaps 5–10 min the second night, but a great majority of them would be cured of sleep disturbance within two nights. Spock emphasized that this policy of letting the baby “cry it out” is recommended only for chronic resistance to sleep in infants up to the age of 1 or 1.5 years.

In 1949, an interesting paper analyzed for the first time sleep disturbances in 100 children (5–14 years old) with primary behavior and emotional disorders at Rockland State Hospital Children’s Group. Sleep disorders were grouped into five categories:

Although no control group was evaluated, the authors state that there is no doubt that a number of these disorders occur more frequently in institutionalized children who suffer from behavior disorders or emotional disturbances. The most frequent disorders were restlessness and minor disturbed states of sleep and enuresis that apparently occurred frequently in rejected children while nightmares, night terrors, and sleepwalking were relatively infrequent [13].

Kleitman in a paper entitled “Mental hygiene of sleep in children” (1949) [14] described perfectly the different aspects of behavioral insomnia of childhood supporting the behavioral approach and stating that “the child is born with certain capacities for learning, including the ability to synchronize, with ease or difficulty, the primitive sleep-wakefulness cycle with diurnal periodicity in his physical and social environment. To establish good sleep habits in children it is necessary to cooperate with the natural tendency to develop a persistent 24-hour rhythm, reinforcing the latter by the customary methods of conditioning.” Moreover, he acknowledged the individual variability for the need of sleep and warned about the recommendations on the amount of sleep needed for the infants and children. He affirmed that “the total time spent in sleep, out of each diurnal period, decreases with age, but not uniformly in all children nor in a particular child at different ages. Tables of hours of sleep provided as a guide to parents are misleading in that the figures suggested for all ages are arbitrarily high. Even if more realistic, such figures could stand only for averages, which, by and large, are meaningless when the individual child is considered.”

During the period between 1950 and 1970, most papers were devoted to the definition of sleep problems in children during the first 3 years of life. Illingworth published several papers attempting to categorize sleep disturbances in infants and children [15, 16]. Concluding one paper on sleep problems in the first 3 years of age, he stated:

Enough has been said to indicate the difficulties and complexities of the problem. He who says that he knows all the answers, or suggests that one particular method is infallible, has little experience of children…. It is not enough merely to instruct the parents to discipline the child, to put him to bed at a fixed time, and, if he objects, to leave him to cry or to drug him. The treatment of sleep problems is not nearly so simple.

The treatment of sleep problems at that time was based on common sense and on the beliefs of a single pediatrician. Illingworth suggested that it is wrong to pick a child up at the first whimper but also that it is essential to go immediately to his/her room when a child wakens with a sudden scream because at these times it would be not only cruel but possibly dangerous not to go to the child. He stated that drugs have little place in sleep problems and phenobarbital is useless with these children. The best drug is chloral hydrate given half an hour before bedtime. Regarding early awakenings, it is humorous to read: “By the age of three he can be made to understand that he must not disturb his parents. Before the age of reason, however, one has to accept this behavior as one of the penalties of having children.”

Different studies then attempted to define the normative parameters of sleep in children as well as the frequency of sleep disturbances [17]. A paper analyzed the frequency of night awakenings in 1957, finding a prevalence of 17 % at 6 months and 10 % at 12 months [18]. In a longitudinal study, Klackenberg in 1968 defined the sleep behavior of children up to 3 years of age [19].

Recent studies have debated on the global decrease of sleep duration in infants , children, and adolescents . The notion that children are sleeping less than they used to is widespread in both the scientific literature and the popular media. A recent study identified a secular decline of 0.75 min per year in children’s sleep duration over the past 100 years, and the greatest rate of decline in sleep occurred for older children and boys, and on school days. This secular decline, variously ascribed to electrification, increased use of technology, and modern lifestyle, is believed to have resulted in many children not getting enough sleep and being chronically sleep deprived [20]. Although there is a lack of consensus regarding what constitutes “adequate” sleep and whether children are in need of more sleep, the results of this study suggest that short sleep duration is associated with different disorders like obesity [21], neurobehavioral and neurocognitive disturbances [22–25], psychiatric disturbances [26], and substance abuse [27].

In the 1980s, the pioneering studies of Mary Carskadon on sleepiness gave impetus to research in children and especially in adolescents. This research paper on sleepiness and adolescent sleep represents another milestone of pediatric sleep. Adolescence is accompanied by striking changes in sleep behavior and in the phenomenology of sleep, paralleled by changes in adolescent sleep structure. Sleep behaviors change during adolescence in response to maturational changes of sleep regulatory processes and competing behaviors leading to insufficient sleep for many teens on school nights. Sleep reduction results in sleepiness, irritability, distractibility, inattention, and lack of motivation and can also threaten learning by affecting the memory formation process [28]. Following the observation on sleepiness in adolescents, interest rose on the delayed sleep phase syndrome and the first case was reported by Weitzman in 1981 in a medical student at the Montefiore Hospital in New York [29]. Other descriptions of delayed sleep phase syndrome in adolescents have been made by different authors [30] and represented the beginning of the studies on circadian rhythm sleep disorders in pediatrics.

An overview of the discoveries and investigations that led to the identification of the main pediatric sleep disorders is presented below.

In 1926, during the Russian Academy of Sciences Congress, the pediatricians Denisova and Figurin presented the results of their first formal pediatric sleep research showing that, several times during sleep, infants presented episodes, lasting for 10–15 min every half an hour, during which respiration and pulse became irregular and fast and small muscles presented numerous twitches. This periodic instability of physiological functions was present in healthy children and the authors concluded that “normal sleep is not a state of rest” [66].

The first description that REMs occur in sleep [67] precedes the landmark study that suggested that REMs represented a “lightening” of sleep and might indicate dreaming, due to the close association with irregular respiration and an increase in heart rate [68].

Before the discovery of REM sleep by Aserinsky and Kleitman in 1953, between 1949 and 1952, Aserinsky observed that sleeping infants exhibited a recurring “motility cycle manifested by ocular and gross bodily activity” paralleling the observation of Denisova and Figurin in 1926 [66].

Aserinsky described “periods of motility” (writhing or twitching of the eyelids) and “periods of no motility.” This observation led Aserinsky and Kleitman to look for a similar phenomenon in adults and they discovered REM sleep. The average duration of the periods of quiescence was about 23 min and of the entire motility cycle was approximately 50–60 min [69].

After the description of REM sleep, many researchers applied the methodology for defining the specific sleep electroencephalographic (EEG) patterns of infants as described by the French school of Dreyfus-Brisac and Monod [70, 71] and that by Parmelee [72, 73] who first showed two distinctive EEG patterns of sleep in infants called “active” sleep (AS) and “quiet” sleep (QS). QS is characterized by preserved chin EMG, few body movements, regular respiration and heart rate, and no eye movements; AS is characterized by REMs, frequent small face and limb movements, irregular respiration and heart rate , and the absence of or minimal chin EMG activity.

The same authors subsequently reported the changes of EEG in infants according to maturation related to conceptional age [74, 75] showing that QS in newborns at term is characterized by one of two EEG patterns: tracé alternant or high-voltage slow (HVS) activity.

Tracé alternant is an EEG pattern in which 3–8-s bursts of moderate- to high-voltage 0.5–3.0-Hz slow waves intermixed with 2–4-Hz sharply contoured waveforms alternate with 4–8-s intervals of attenuated mixed frequency EEG activity; because this pattern alternates between activity and much less activity, it is considered to be “discontinuous.” In contrast, HVS consists of continuous moderately rhythmic 50–150-μV, 0.5–4-Hz slow activity, without the bursting activity of the tracé alternant. HVS represents the more mature pattern of QS in infants.

In 1970, Dreyfus-Brisac observed that active (REM) sleep could be identified in polygraphic tracings by 32 weeks of gestation because of the presence of frequent body movements, irregular respiration, and REMs while the eyes were closed. In 1972, Parmelee and Stern recognized QS or non-REM sleep after 36 weeks of gestation and characterized it by the presence of closed eyes with no eye movements, no body movements, and very regular respiration.

The first description of the ontogenesis of sleep states has been published in Science in 1966 by Roffwarg, Muzio, and Dement. Dement and Roffwarg tried to answer the question at what age do humans start having dreams. Observing infants, they confirmed the richness of their REMs; they therefore supposed that REM sleep was fundamental for the optimal development of the CNS. Roffwarg and colleagues found infants spent half of their total sleep time in REM sleep, leading to the theory that REM sleep must play an important role in the development and maturation of the immature brain [76]. At the same time, sleep researchers in Prague described the development of sleep in infancy showing that QS (regular breathing with frequency of 30 min, closed eyes without movements, disappearance of body movements, spindles and slow waves in EEG) alternated with AS (irregular respiration, eyes alternatively closed, half-open or there were movements of bulbus oculi, increased frequency of body movements) in about 50–60-min intervals. These authors stated that the most striking changes took place in the first 12 weeks of life [77].