National data on predictors of child mental health symptoms highlighted a small number of significant risk factors, situated in the family context and present from a very young age. This knowledge is informing population-level, randomized, prevention trials of family support programs.

In childhood, mental health problems primarily consist of behaviour and emotional problems. These affect one in every seven children (i.e. 200 000 in Australia). Left untreated, up to 50% of preschool problems continue through the childhood years. Because of their high prevalence, population-based approaches will be needed to reduce their associated burden. The aim of the present study was therefore to identify evidence-based preventive interventions for behavioural and emotional problems of children aged 0-8 years. Randomized controlled trials of preventive interventions for behavioural and emotional problems were located by searching standard clinical databases and systematic reviews. The authors determined which programmes were effective and ineffective, dividing the effective programmes into those with high or low risk of trial bias. Among effective programmes, the most promising for delivery in Australian contexts were identified, selected for their strength of evidence, sample comparability to Australia's population, and programme compatibility with Australia's service system. Around 50 preventive interventions have been evaluated in randomized controlled trials. Most targeted children's behavioural problems, and a few targeted emotional problems. Three US programmes have the best balance of evidence: in infancy, the individual Nurse Home Visitation Programme; at preschool age, the individual Family Check Up; at school age, the Good Behaviour Game class programme. Three parenting programmes in England and Australia are also worthy of highlight: the Incredible Years group format, Triple P individual format, and Parent Education Programme group format. Effective preventive interventions exist primarily for behaviour and, to a lesser extent, emotional problems, and could be disseminated from research to mainstream in Australia, ensuring fidelity to original programmes. Future research should develop programmes targeting emotional problems, and replicate effective programmes for behaviour problems in quality population translation trials. Randomized trial methods in staged roll-outs can determine population cost-benefits for children's mental health without delaying dissemination.

In these large child population cohorts, sleep duration did not predict obesity up to age 6-7 years. Current trials of sleep interventions to prevent or manage obesity in young children may be premature.