Researchers at the Urban Institute said 81.5 percent of children were enrolled in Medicaid and the Children's Health Insurance Program in 2009, and that figure increased 5.5 percentage points by 2011 to 87 percent.
The increase was likely attributable to state and federal efforts to raise awareness of the availability of public insurance programs for kids, as well as increased enrollment assistance for parents, the researchers said.
In total, 19 states and the District of Columbia had participation rates of 90 percent or higher for children's health insurance, while four states -- Alaska, Montana, Nevada and Utah -- had rates below 80 percent.
Nearly 37 percent of all eligible-but-uninsured children live in California, Florida or Texas.
If additional enrollment efforts were targeted in those states, it could profoundly reduce the percentage of children nationwide who are uninsured, the study authors said.