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

Background: The study examined developmental trajectories of prosocial behaviours, internalising and externalising behaviour problems in children with intellectual disabilities (ID) between pre-school and middle childhood. Method: Growth models examined the best-fitting trajectories for internalising and externalising behaviour problems, as well as prosocial behaviours, in 555 children with ID between the ages of three and 11 years from the UK Millennium Cohort Study. Models were also fitted to examine the association of child outcomes with time-varying maternal psychological distress and life satisfaction. Finally, models were extended to compare trajectories with typically developing children. Results: Externalising behaviour problems and prosocial behaviours generally improved, whereas internalising problems did not change systematically over time. A cubic trend indicated a slowing down of improvement between ages 5 and 7 for prosocial behaviours and externalising problems. Maternal psychological distress positively co-varied with internalising and externalising behaviour problems over time. Life satisfaction was not related to changes in child behaviours over time. Compared to behavioural trajectories in typical development, intercepts were worse and trajectories also differed in the ID group. Conclusions: 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.