In this study, the relationships between child social functioning, parenting stress, and Part C Early Intervention (EI) enrollment were examined in 227 ethnically and racially diverse, low-income families of 15- to 27-month-old children. All toddlers in the sample were identified with or at high risk for developmental delay via universal screening in primary care; 41.4% were enrolled in EI at the time of study data collection and 83.3% ultimately enrolled in EI before turning 3 years old. Generalized linear mixed model results indicated no direct relationship between EI enrollment and parenting stress, but a significant inverse association was found between child social functioning and parenting stress (β = −0.61, p = .005) that was moderated by EI enrollment (p < .001). This suggests potential benefits of timely referral and access to EI for families of children at risk of developmental delay in historically underserved communities. Furthermore, exploratory bivariate analyses indicated that clinically elevated parenting stress related to higher worry about the child’s development and higher M-CHAT-R/F scores; EI enrollment was related to parents not working outside the home, older age of both parent and child, and lower child social functioning level. (author abstract)