Researchers have found that more than 3% of U.S. children and adolescents are uninsured or underinsured at some point during any given year, despite having at least one parent with health insurance. That translates into almost 3 million U.S. children with no medical care at all and no access to prescription drugs. Slightly more than half of that number qualify for public coverage but aren't enrolled, the study found. Overall, more than 9 million U.S. children are uninsured, and approximately 18 million have a coverage gap at one time or another, according to the study.