“Is there cause for concern? Absolutely,” Dr. Sean O’Leary, the vice chair of the academy’s infectious diseases committee, said in an interview on Monday night. “What’s driving the increase in kids is there is an increase in cases overall.” Children have accounted for a greater percentage of overall cases since the vaccines became widely available to adults, said Dr. O’Leary, who is also a professor of pediatrics at the University of Colorado School of Medicine and Children’s Hospital Colorado.