Bolstered by the federal health care law, the number of lower-income children getting health coverage continues to rise, a study found.

In 2014, the first full year of the law’s implementation, 91 percent of children who were eligible for Medicaid or the Children’s Health Insurance Program were enrolled, according to the study by researchers at the Urban Institute. In 2013, that figure was 88.7 percent, and only 81.7 percent in 2008. Medicaid and CHIP are federal-state health coverage programs for lower-income residents, but CHIP provides coverage for children whose families earn too much to qualify for Medicaid.

Given that coverage rates were already quite high for children, “I was surprised to see gains to such an extent in 2014, and for that to happen for so many different kinds of children and in so many different places,” said Genevieve Kenney, co-director of the Urban Institute’s Health Policy Center who was an author of the study.

The biggest coverage increases occurred in states that expanded Medicaid to adults with incomes up to 138 percent of the federal poverty level (about $33,500 for a family of four), probably a spillover effect as adults signed up and learned that their children were eligible, too. So far 31 states and the District of Columbia have adopted the Medicaid expansion.

The coverage increase among children eligible for Medicaid and CHIP mirrors changes in the non-insured rate for children overall, which fell from 7 percent in 2013 to 5.8 percent in 2014, the researchers noted.

There were coverage gains for all types of children from 2013 to 2014, including those of different ethnic groups, ages and family incomes.

But progress has been slower for some groups, including adolescents ages 13 to 18.