Our understanding of the mental health of infancy and early childhood (0–4 years of age) is undergoing a transformation. Traditional psychodynamic developmental accounts are transforming into operationalised, ethological accounts of cognitive processes and adult–child interaction. Intrauterine and early-life development are being increasingly implicated in the aetiology of both child and adult mental illness, while psychological trauma and adversity in this period are being associated with physical as well as mental ill health. The concept of developmentally specific psychiatric syndromes, which underpinned diagnosis for these children, is being eroded. In treatment, there has been increasing recognition of the economic advantages of early intervention, and primary care has engaged extensively with parent training, with good effect. However, in the UK secondary care activity with 0- to 4-year-old children declined by 16.9% between 2006 and 2009, and an unpublished survey conducted by the Royal College of Psychiatrists in 2012 found that 28% of UK child psychiatrists believed that general child and adolescent mental health services (CAMHS) were not appropriate for the problems this group present. This chapter therefore presents an overview of the psychiatry of this age range, with the intention of improving awareness of the importance of mental health in children under 5, exploring the ways in which child psychiatrists may currently contribute, and indicating likely future directions for mental healthcare. A developmental psychopathology approach will be taken, to allow consideration of this group in terms of both current psychopathology and risk (and resilience) factors affecting later health difficulties.

Diagnosis and epidemiology

Diagnosis

The frequency of disorders in 0- to 4-year-olds cannot be determined without an agreed way to detect and classify them, and unfortunately diagnoses in this age range have been contentious. The traditional approach has been to emphasise differing developmental trajectories and adult– child (especially parent–child) relationships across broad behavioural domains, leading to differing forms of classification from those used in other population segments. In classic infant psychiatry, five domains were proposed as defining developmentally specific syndromes:

The first of these has now been extended into the category of autism spectrum disorders and is recognised as a lifespan diagnosis.