Abstract
The development of distinct restricted and repetitive behaviors and interests (RRBIs) is well-studied in autism, but their relationship to cognitive and affective development in young autistic children is unknown. This cross-sectional study examined how higher-order RRBIs (e.g., circumscribed interests and insistence on sameness) and sensorimotor RRBIs (e.g., stereotyped movements and sensory preoccupations) relate to concurrent developmental level, executive function, temperament, and internalizing and externalizing behaviors in autistic toddlers and preschoolers. 143 2- and 4-year-old autistic children with developmental levels of at least 12 months completed a battery of executive function tasks, and caregivers completed interviews and questionnaires regarding their children's autistic features and affective functioning. Higher-order RRBIs, but not sensorimotor RRBIs, were related to age and developmental level. In the 2-year cohort, discomfort and executive function related to higher-order RRBIs, as well. Hyperactivity related to sensorimotor RRBIs in both cohorts, and discomfort also related to sensorimotor RRBIs in the 4-year-olds. These findings suggest that temperamental markers and features of mental health conditions may contribute to the expression of distinct RRBI subdomains. Child cognitive capacity may also underlie parental ability to report on RRBIs for young children. This study highlights the importance of distinguishing RRBI subdomains in young autistic children due to their distinct relationships to functioning and wellbeing.