More than 9 million children across the country are uninsured, according to the Journal of American Medical Association.

Researchers at the Oregon Health and Science University studied about 40,000 of those children and found that many come from families with working parents who do have insurance coverage.

“We found about 3 percent of children in the U.S. are uninsured with an insured parent. And that translates to over 3 million children,” said Dr. Jennifer DeVoe, who's in the Department of Family Medicine at the Oregon Health and Science University in Portland, Ore.

The study appears this week in the Journal of the American Medical Association.

“The largest predictor of children being uninsured with an insured parent was being in the middle income, earning somewhere between about $25,000 and $75,000 a year for a family of four,” DeVoe said.

Some families' earn too much to qualify for state insurance programs, but not enough to afford adding their kids to employer-sponsored policies.

Other families do qualify for help, but don't sign up for numerous reasons, including because the enrollment process can be confusing.

Fran Denham is covered through her husband’s health policy, but it was too expensive to add their grandchild, whom they raised.

“It is very stressful to have a kid that you’re responsible for and you can’t take care of him the way you need to,” Denham said. “You just hope and hope and hope that nothing happens bad, because if it does, you're up that creek – that nasty, dirty creek – without a paddle."

The four-year study also identified several factors associated with families that have an insured parent and uninsured children, including the likelihood the family is Hispanic, lives in the southern or western United States and has parents who did not finish high school.