Mental-health problems are estimated to affect up to 20% of children in modern Western societies. They are divided into externalising problems such as aggression and 'oppositional defiance' and internalising ones such as depression and anxiety. Early mental-health problems often continue through childhood and adolescence into adulthood and can cause problems socialising, learning difficulties, school dropout, substance abuse, poor vocational outcomes, family violence and suicide. A three-year study of 589 children in Australia found that 'the consistent and cumulative predictors of externalising behaviours were parent stress and harsh discipline. Predictors of internalising behaviours included small family size, parent distress and parenting.'
Bayer, Jordana K. ... [et al] - Early childhood aetiology of mental-health problems: a longitudinal population-based study Journal of Child Psychology and Psychiatry November 2008, 49(11), 1166-1174