Background: Research indicates that having child siblings is positively associated with theory of mind (ToM) in typically developing children. As ToM is important to everyday social behaviours it is important to extend this research to examine whether there are similar sibling effects for children with autism spectrum disorders (ASD).
Methods: Theory of mind and executive functioning abilities of 60 children clinically diagnosed with ASD were assessed with batteries of standard tasks. Verbal mental age (VMA) and severity of autism symptoms were also measured together with number of child-aged siblings (1 to 12 years) and position in the sibling constellation.
Results: Having older siblings was a significant negative predictor of ToM performance for children with ASD, even after controlling for age, VMA, executive function and autism symptom severity. A weaker ToM benefit of younger siblings was not statistically significant independently of control variables.
Conclusions: In sharp contrast to findings for typically developing preschoolers, having an older sibling was a disadvantage for ToM development in children with ASD. Conceivably, older siblings may over-compensate for their younger ASD siblings in social interactions, thereby limiting opportunities for social-cognitive growth. Parental attitudes, family resources, cultural norms and access to educational interventions may also conceivably be relevant and clearly warrant further research.