Using 2007 data, the New England Journal of Medicine (NEJM) released a study examining underinsurance among children.  The study found that 19.3 percent of all children, or 14.1 million individuals, were underinsured in 2007.  Underinsurance was higher among children covered through private insurance than among those enrolled in public insurance programs at rates of 24.2 percent and 14.7 percent, respectively.  In addition, the study found that the most common reason for underinsurance was high out-of-pocket costs.

From the report:

Policy discussions on children’s health insurance have been devoted largely to reducing the number of uninsured children. As compared with children who have health insurance, those lacking insurance are more likely to have needed care that is delayed or forgone; less access to preventive, specialist, or long-term care; lower utilization rates; care that imposes a high financial burden on their families; and poor health outcomes. Children with intermittent health insurance (i.e., periods without insurance throughout the year) are at greater risk for delayed care, unmet health care needs, lack of a usual source of care, and nonreceipt of well-child care.

Full report: Underinsurance among Children in the United States  

The New England Journal of Medicine. (2010). Underinsurance among children in the United States. Kogan, M.D., Newacheck, P.W., Blumberg, S.J., Ghandour, R.M., Singh, G.K., Strickland, B.B., and  van Dyck, P.C.