It's great when kids take their vitamins — as long as the right kids get them. Researchers at the University of California, Davis, found that about one-third of U.S. children ages 2 to 18 take vitamin and mineral supplements, but most of those kids come from higher-income families and are more likely to eat consistent and nutritious meals. Lower-income kids, who have the worst diets and need supplements the most, are the least likely to get them. Part of the problem is policy: 55% of U.S. infants are eligible for a federal nutrition program, but it provides food, not vitamins.