Background: The developmental-ecological model highlights the contextual environments that influence children's emotional and behavioral adjustment. No previous research considers neighborhood characteristics when examining the influence of extended family members. Objective: This study investigates the characteristics of neighborhoods where extended family households reside, and the confounding and moderating effects of extended family household structure and the neighborhood influences of income and co-ethnic concentration levels. Method: Data come from the Los Angeles Family and Neighborhood Study and the decennial census. The analytical sample includes 1553 children between the ages of 3 and 11 years, clustered in 1191 households in 65 census tracts. This study uses multilevel linear regression modeling. Results: Extended family households are more likely than nuclear families to live in lower-income neighborhoods, but with similar proportions of co-ethnics. Children in extended family households show higher levels of both internalizing and externalizing behaviors compared to children in nuclear families, an effect not explained by their neighborhood environments. Extended family members moderate the neighborhood effects, boosting advantages within co-ethnic concentrated neighborhoods. With a higher proportion of co-ethnics in their neighborhoods, children in extended families show lower levels of externalizing behaviors compared to children in nuclear families. Conclusion: Co-resident extended family members not only predict child internalizing and externalizing behavioral problems but also moderate their neighborhood environments. This study provides policy implications, highlighting the potential of extended members to promote child development.