ABSTRACT Importance Child behavior problems have been shown to contribute to caregiver distress and vice versa among youth with developmental delay (DD). However, studies have not examined these associations among children and caregivers from underrepresented ethnic/racial backgrounds. Furthermore, research has not explored how associations function differently following internet-delivered treatment or based on the level of acculturation and enculturation. Objective We examined bidirectional associations between caregiver distress (i.e. symptoms of depression, anxiety, and stress) and externalizing and internalizing behavior problems in 3- to 5-year-old children with DD from underrepresented ethnic/racial backgrounds. We also examined the impact of internet-delivered Parent–Child Interaction Therapy (iPCIT) and the moderating role of acculturation and enculturation on these bidirectional associations. Method Children aging out of early intervention services (n = 150) and their primary caregiver were randomized to receive iPCIT or referrals as usual (RAU) in the community. Results Findings provide support for bidirectional associations between child internalizing behavior problems and caregiver depressive symptoms, although there were fewer significant associations among families randomized to iPCIT compared to RAU. Weaker associations were observed among families with higher levels of enculturation, whereas stronger associations were observed among families with higher levels of acculturation. Conclusions Results highlight a sensitive period from age 3.5 to 4 years old for bidirectional associations between caregiver distress and child behavior problems and highlight the importance of addressing family cultural values during treatment. Findings also suggest the utility of internet-delivered behavioral parenting interventions in weakening the effect of child behavior problems on caregiver distress and vice versa.