Worldwide, about 780 million children may have some degree of intellectual disability between birth and 5 years of age [9]. There is considerable variance in aetiology of intellectual disability; these include genetic, perinatal (e.g. birth asphyxia) and infectious causes, malnutrition, micronutrient deficiencies, head injuries, lead poisoning, prematurity, low birth weight, malignancies, and potentially the pernicious effects of poverty, child abuse and child neglect [10]. Early intervention studies have largely focused on children with a combination of the above risk factors. A recent comprehensive review of 32 controlled studies reported that efficacious interventions used a combination of specific intervention procedures, including (1) parent involvement in intervention, including ongoing parent coaching that focused both on parental responsivity and sensitivity to child cues and on teaching families to provide the infant interventions, (2) individualization to each infant’s developmental profile, (3) focusing on a broad rather than a narrow range of learning targets, and (4) temporal characteristics involving beginning as soon as the risk is detected, and providing greater intensity and duration of the intervention [10]. An earlier comprehensive review of studies in the field found that improvements persisted into late adolescence and adulthood. Early intervention programs that provided more intensive educational services, started earlier and lasted longer appeared to be most beneficial. Similarly, programs that directly targeted the child’s everyday experiences, rather than indirectly sought to change this through increasing parental competency or the quality of the child’s living conditions, yielded more immediate and greater effects [11]. Overall, there is unequivocal evidence for both the short- and long-term effectiveness of early intervention, with effect sizes in the modest range (from 0.44 to 0.75 SD). It is important to note that most of these results were produced by ‘model’ programs with considerable resources and highly skilled staff. The extent to which similar outcomes can be achieved by programs embedded within existing community resources remains to be seen [10–12].

Autistic spectrum disorders (ASD) are a heterogeneous group of disorders characterized by a qualitative/quantitative impairment in reciprocal social interaction, a qualitative/quantitative impairment in language and communication and a restricted repertoire of interests/stereotypes together with problems in functional, adaptive and flexible behaviours. Owing to its developmental nature, disability limitation and improving functionality is the mantra. Early intervention focuses on enhancing cognitive, communication and social skills while minimizing core autistic symptoms and other comorbid problem behaviours. Pretreatment variables that seem to predict later outcome are IQ, presence of imitation ability, language, younger age at intervention, severity of symptoms and social responsiveness or ‘joint attention’ [13].

Among the most thoroughly evaluated are programs involving early intensive home-based behavioural intervention (EIBI), championed by Lovaas (1987) [14], who demonstrated that early intervention with parents as co-therapists works This has been followed by several other types of intervention, all of which have reported varying degrees of success. Most have a mix of developmental, behavioural and educational approaches. Applied behaviour analysis (ABA) forms the basis of behavioural techniques such as EIBI and other approaches such as Pivotal Response Training, Discrete Trial Training and Verbal Behaviour that form part of most early intervention programs for children with autism [15–19]. A recent comprehensive review of literature in the area was undertaken by Howlin and colleagues [20], who compared and contrasted key studies in the field. They report that the interventions based on ABA, particularly those involving home therapy and beginning in the preschool years, have been most comprehensively studied and have the best established evidence base. The EIBI approach is highly prescriptive, with detailed manuals provided to guide and monitor treatment. Learning sessions are provided in a one-to-one discrete trial format, focusing on the systematic teaching of measurable behavioural units, repetitive practice, and structured presentation of tasks from the most simple to the more complex. Alternative approaches have included intensive, parent-directed interventions; reduced intensity EIBI programs; eclectic, public-school-based programs [21]; specialist autism-school-based programs [22] and a mixture of different interventions including those nonintensive ones with a focus on communication and joint social interaction [23]. Most studies have been of 2–6 year durations and demonstrated varying degrees of change in outcome measures, such as improvement of IQ over time, improvement in Vineland Adaptive Behaviour Scale (VABS) [24] scores, improvement of expressive and receptive language skills, reduction in problem behaviours, more positive parental reports and an improvement in school integration following intervention. Early intervention resulted in gains persisting through to adolescence. However, the most substantial gain occurs in the first year of intervention followed by modest gains thereafter.

Asperger’s syndrome is part of ASD with a qualitative (not quantitative) impairment in communication and without associated intellectual disability. Owing to this, diagnosis is often delayed, which is unfortunate as the syndrome is often associated with greater psychological and medical comorbidities and significant social impairment. Early intervention strategies focus on (1) developing social skills delivered in the form of a group approach that includes focused instruction on actual target behaviours (such as eye contact), training in social perception, as provided by computer packages such as Let’s Face It, or Mind Reading: An Interactive Guide to Human Emotions, and allowing the opportunity to practice skills they learn in varied, naturalistic contexts for generalization and maintenance, (2) encouraging adaptive problem-solving strategies and reducing maladaptive patterns of behaviour, and (3) teaching more effective communication. Early intervention in ASD with psychopharmacological agents for both core symptoms and comorbidities include SSRIs like fluoxetine and low-dose antipsychotic agents such as risperidone [25].

ADHD is a common neuro-developmental-behavioural disorder of childhood with a 3–6% prevalence rate [26]. Core symptoms include developmentally inappropriate impulsiveness, inattention and hyperactivity which cause significant functional impairment in more than one setting. Eighty percent of all lifetime ADHD begins in the pre/primary school years and symptoms often persist through adolescence and into adulthood, with varying symptom expression and disabilities at different developmental stages [27]. Although there has been some controversy about the validity of the diagnosis, there is very robust evidence for the existence of ADHD and the associated significant disability, including poor self-regulation, planning and execution that impacts across the life span [28, 29]. Comorbidity with learning difficulties, autism spectrum disorders, tics, ODD/CD, mood disorders and substance use later in life is not uncommon. Initial evaluation should involve a full medical, developmental and educational history, including appropriate liaison with preschool/school, exploring ADHD-related symptomatology, comorbidity and its impact on the child’s life. Psychological/behavioural intervention is recommended as an initial treatment for preschool children if ADHD symptoms are mild with minimal impairment, the diagnosis of ADHD is uncertain, parents reject medication treatment or there is marked disagreement about the diagnosis between parents or between parents and teachers. In general, parents are involved in 10–20 sessions of 1–2 hours in which they are: (1) given information about the nature of ADHD; (2) taught how to establish a positive relationship with their child through play and child-centred activities; (3) taught to attend more carefully to their child’s misbehaviour and when their child complies; (4) able to establish a home token economy including encouraging praise, reward and incentives for appropriate behaviours; (5) given guidance in the use of effective limit setting and clear instruction giving; (6) able to use time out effectively, (7) manage noncompliant behaviours in public settings; (8) use a daily school report card and (9) anticipate future misconduct. Efficacy of the above has been demonstrated in a large study using the ‘Incredible Years’ parenting program as an early intervention strategy for preschool children with ADHD [30, 31].

Pharmacotherapy consisting of using various short- and long-acting preparations of stimulants (methylphenidate and amphetamines) has the best and most robust evidence of efficacy followed by atomoxetine and clonidine. There is some evidence for the efficacy of stimulants in the preschool years. However, the dose should be titrated more conservatively in preschoolers than in school-age children and lower mean doses may be effective as they metabolize stimulants slower. Evidence is limited with other medications. Appropriate premedication evaluation, parental counselling around effects, side effects, duration of treatment and close monitoring of progress and side effects is vital [28, 31, 32]. The largest intervention trial for ADHD to date was the Multimodal Treatment Study of Children with ADHD [33], which found that while medication was clearly the best intervention for core ADHD symptoms to 24 months; intensive behaviour therapy was associated with improvements in some key associated symptoms such as oppositional behaviour, social skills and family functioning. Responses to multicomponent interventions are better than single-focus therapies.

Left untreated, the long-term prognosis for children with ADHD is poor. They are at a much greater risk of experiencing problems in the educational, personal and social domains and subsequently developing conduct problems, mood disorders, substance abuse and interpersonal and occupational difficulties that can persist into adulthood. Early intervention could possibly mitigate these long-term effects. However, robust evidence for that is currently lacking [28, 30].

Lifetime prevalence of disruptive behaviour disorders (DBD) in children is about 6.8%, of which ODD makes up about 3% and CD 3–5% [6]. Children who develop a stable pattern of oppositional behaviour during their preschool years are most at risk. They have substantially strained relationships with their parents, teachers and peers, and have high rates of comorbidity with ADHD and mood disorders. They are also at greater risk of developing ODD and CD in later childhood and antisocial personality disorder (ASPD) during adulthood. The need for early intervention is therefore self-explanatory, with parenting programs generally viewed as an essential component. Programs that have demonstrated efficacy in various age groups include the Nurse Home Visitation program in infancy and Family Check Up and Head Start program in the preschool years, which found that positive and proactive parenting skills correlated with changes in child disruptive behaviour and reduction of delinquency. The Triple P (Positive Parenting Program) and Incredible Years parenting series use self-directed, multimedia, parenting and family support strategies to prevent severe behavioural problems in children by enhancing the knowledge, skills and confidence of parents. These programs are most appropriate for parents whose children appear to be in the early stages of emotional and/or behavioural problems. School-based programs that focus on antibullying, antisocial behaviour or peer groups are other effective strategies. Parent Child Interaction Therapy (PCIT) is a promising intervention for CD. Other programs that have shown promise in the field include the Scallywags service, a multicomponent, early intervention scheme, offering support in the educational and home setting of children, aged 3–7 years, and the Fast Track Intervention, a 10-year program (kindergarten to 10 years) addressing parent behaviour management, child social cognitive skills, reading, home visiting, mentoring and classroom curricula. The Fast Track Intervention was the first to demonstrate that long-term intervention can prevent development of CD in high-risk children and the effects can be sustained for at least 2 years after the cessation of the intervention [34–37].