In this study we investigate the effect of Medicaid on children's health, as measured by the incidence of ambulatory care sensitive (ACS) hospitalizations in the USA. The use of ACS hospitalizations is a unique contribution of our study. ACS discharges are known to be sensitive to better primary care and greater medical intervention and are objective measures of children's health. The results of this analysis were mixed. We found relatively robust evidence that the Medicaid expansions decreased the incidence of ACS hospitalizations among children age 2-6 from very low-income areas. For other groups of children, our results were less consistent. There was some evidence, although not uniform, that the Medicaid expansions improved the health of children age 2-6 from what we refer to as near-poor areas, areas with a median family income between $25,000 and 30,000. For older children, age 7-9, we found little evidence that the Medicaid expansions improved their health.