Although a national consensus has emerged regarding the importance of extending publicly-funded health insurance coverage to low-income children under the State Children's Health Insurance Program (SCHIP) and Medicaid, substantial numbers of eligible children remain uninsured. This study examined whether extending insurance coverage to low-income parents influenced the enrollment among children. Data were obtained from the Current Population Survey. The change in child and parent Medicaid participation rates between 1990 and 1998 was measured for each of three groups of states, comparing the net differences in changes in states with early expansions (Hawaii, Oregon, and Tennessee) to the changes in states with late or non-Medicaid expansions (Delaware, Massachusetts, Minnesota, New York, Vermont, and Washington) and to states with no expansions by 1998 (all other states). The key findings indicated that most children in families with incomes below 200 percent of poverty are already eligible for Medicaid or SCHIP, but 25 percent of eligible children remained uninsured in 1998. Family-based Medicaid expansions that include parents can increase Medicaid enrollment among children who already are eligible for Medicaid but are unenrolled. States can reduce the proportion of persons who are uninsured through broad Medicaid expansions that include parents. Broad Medicaid expansions that include parents can substantially improve health care access and utilization for both adults and children. (A description of the study's methodology and a technical discussion of the effects of broad expansions on young children's Medicaid enrollment are appended.) (KB)