Publicly funded adult health insurance through the Affordable Care Act (ACA) has had positive effects on low-income adults. We examine whether the ACA's Medicaid expansions influenced child development and family functioning in low-income households. We use a difference-in-differences framework that exploits cross-state policy variation and focus on children in low-income families from a nationally representative, longitudinal sample followed from kindergarten to fifth grade. The ACA Medicaid expansions improved children's reading test scores by approximately 2 percent (0.04 SD). Potential mechanisms for these effects within families are more time spent reading at home, less parental help with homework, and eating dinner together. We find no effects for children's math test scores or socioemotional skill development.