The benefits of physical activity and active play for children and young people are well established. However, there is a lack of physical activity research involving children and young people with intellectual disabilities. This study investigated habitual physical activity and recess play behaviour in 70 5- to 15-year-old participants with intellectual disabilities using objective methods (accelerometers) and systematic observation techniques. Results showed that few children were active enough to benefit their physical health (23% of the cohort). No differences in habitual physical activity, sedentary behaviour, or recess play behaviours were observed between boys and girls. Participants spent most of their recess time alone or playing in small groups, with no participants engaging in large group play. Older participants spent more recess time playing in small groups rather than playing alone and participants with Autistic Spectrum Disorder spent more time engaged in active pursuits and less time standing than non-Autism Spectrum Disorder participants. Positive correlations were observed between time spent alone and physical activity. These findings contrast with those typically observed in a mainstream school setting. In conclusion, interventions designed from formative research are needed to promote physical activity within this population. Implications for school psychologists are discussed.