This study examined the natural social interest of 193 (95 boys, 98 girls) typically developing preschoolers aged 41 to 77 months (M = 61.71 months, SD = 8.48 months) toward their included peers with autism spectrum disorder (ASD; N = 16, M = 66.8, SD = 8.80). A hierarchical linear model examined the role of endogenous (within-child) and exogenous (environmental) variables in explaining typically developing children's natural social behaviors. Results indicated the significant contribution of three variables: (a) typically developing children's prosocial behaviors, (b) teachers' attitudes about their training regarding inclusion, and (c) areas of inclusion support needed by the specific child with ASD. Discussion highlighted possible interactions among these variables within the social-ecological theoretical framework, for explaining peer relations of typically developing children with peers with ASD in regular preschools.