Behaviour, cognition, and autism symptoms and their relationship with sleep problem severity in young children with autism spectrum disorder

•First paper to examine sleep in 2- to 5-year old autistic children by categorising sleep into three groups based on sleep problem severity.•Shows that in young autistic children severe sleep problems are associated with increased social withdrawal and overall behavioural problems.•Shows that in 2- to 5-year old autistic children, sleep problems in general are associated with poor attention.•Shows that in this age group, autism severity and cognition likely do not make a significant contribution to poor sleep.•Has implications for identifying risk for poor sleep as well as developing interventions for children in this age group.