A recent report concluded that many children have less-than-optimal blood levels of vitamin D. In the fall of 2008, the American Academy of Pediatrics announced that it had doubled its recommendation to 400 IU daily starting in the first few days of life. Milk, formula, and fortified soy milk are the biggest sources of D in most kids' diets, so make sure that your child drinks enough. If you're breast-feeding, talk to your doctor about supplements for your infant. Yet another reason to keep your kids from overeating: Excess body fat traps vitamin D, leading to lower levels of it in the blood.