Developmental trajectories of behaviour problems and prosocial behaviours of children with intellectual disabilities in a population-based cohort.

Over an 8-year period, externalising behaviour problems and prosocial behaviours of children with ID tended to improve. These behavioural improvements slowed between five and seven years, possibly coinciding with school-related environmental changes. Children with ID significantly differ from children with typical development in both the initial level of difficulties (exhibiting higher externalising and internalising behaviours, and lower prosocial behaviours) and subsequent development as they age, showing comparatively lower decreases in both externalising and internalising behaviours, and lower increases in prosocial behaviours. Findings also highlight the significant role of maternal mental health problems in the trajectory of child behaviour problems.