The number of uninsured children in the U.S. increased by more than 400,000 between 2016 and 2018, with 15 states showing significant increases in the number and/or rate of uninsured youth, according to a new Georgetown University report .

The report, issued by the university's Center for Children and Families, found that there are now more than 4 million uninsured children. And children's participation rates in Medicaid/CHIP – Children's Health Insurance Program – dropped from 2016 to 2017 for the first time since participation was first measured in 2008.

According to the authors, this drop in coverage is largely attributable to the Trump administration's actions, which include Medicaid cuts, a repeal of an individual mandate penalty and delayed the extension of CHIP for many months in 2017.

"Recent policy changes and the failure to make children's health a priority have undercut bipartisan initiatives and the Affordable Care Act, which had propelled our nation forward on children's health coverage," Joan Alker, executive director of the Georgetown University Center for Children and Families, said in a press release .

Approximately half of America's uninsured children live in six states: Texas (21.5%), Florida (8.4%), California (7.4%), Georgia (5.4%), Arizona (3.6%) and Ohio (3.3%). Texas has the highest uninsured rate, with 11.2% of youth lacking insurance in 2018, compared to the national average of 5.2%.

Regionally, nearly 53% of children without health insurance live in Southern states.

The following 15 states saw statistically significant increases in either the number or rate of uninsured children from 2016 to 2018: Alabama, Arizona, Florida, Georgia, Idaho, Illinois, Indiana, Missouri, Montana, North Carolina, Ohio, Tennessee, Texas, Utah and West Virginia.

North Dakota was the only state to see an increase in coverage over this time period.