An online poll of about 2,000 adults indicated 6 percent of the parents responding delayed a medical appointment or buying medications for their children, the University of Michigan said in a news release. About two-thirds of those surveyed indicated they were parents.

"At the national level, these poll findings indicate that more than 4 million children have had a medical visit or medications postponed because of high gas prices," said Dr. Matthew Davis, director of the university's C.S. Mott Children's Hospital National Poll on Children's Health.

Low-income families and families living far away from children's healthcare providers were particularly likely to say they'd missed a child's medical visit due to gas costs, the survey said.