To better understand the impact of children's autism spectrum disorder (ASD) severity on families, we evaluated pathways through which ASD severity affected child sleep quality, caregiver strain, and caregiver sleep quality. In a cross-sectional analysis through the U.S.-wide Simons Foundation Powering Autism Research for Knowledge (SPARK) cohort. Participants were caregivers of dependents with ASD aged 3-17 years (N = 3150). We found that increased severity strongly affects caregiver strain and child sleep quality. Child sleep quality was a minor mediator of increasing caregiver strain. Caregiver sleep quality depended on ASD severity only through child sleep quality and caregiver strain. Interventions aimed at improving child sleep quality or reducing caregiver strain could positively impact families of children with ASD.