Racial–ethnic disparities in the diagnosis of certain developmental disabilities (DDs), such as autism spectrum disorder (ASD), contribute to delayed treatment for Latinx children. Although recent data suggest the disparities are mitigated over time, Latinx children are still less likely to have an ASD diagnosis, and those from low-income families are disproportionately affected. To build on previous research emphasizing these racial–ethnic disparities, this study focused on families in vulnerable or underserved communities, including female-headed and low-income households. Multiple waves of the Fragile Families and Child Wellbeing Study were analyzed, so that this sample represents populations mainly served by social workers. After controlling for demographic and socioeconomic factors, and behavioral health symptoms, authors estimated the likelihood of receiving a diagnosis for a particular developmental disorder and overall DDs. Compared with children of non-Latina White mothers, children of Latina mothers were less likely to have an ASD diagnosis. Findings confirm the lingering racial–ethnic gaps in diagnoses, even among female-headed households and low-income families. Further, authors suggest interventions addressing systematic and cultural barriers for equitable diagnosis of DDs that target pediatricians and other behavioral health providers, teachers, and Latinx families and communities.