Research on public health insurance expansions has typically focused on those targeted by the expansions; the authors estimate the spillover effects of parental Medicaid expansions on the insurance coverage of their children. Expanding parental Medicaid eligibility may increase participation by already-eligible, uninsured children by increasing the value of Medicaid enrollment for the entire family. However, parental expansions may also generate crowd out from private coverage. Using the Survey of Income and Program Participation during a period of major parental Medicaid expansions, the authors find substantial effects of the expansions on the Medicaid participation of children, with evidence of crowd out among some subsamples.