But for some reason that’s not entirely clear, drinking milk can decrease iron stores; kids who slurp up lots of milk tend to have severe iron deficiency. The solution? More specific guidelines for how much milk children should drink, advice that doesn’t currently exist in any helpful form for parents. The American Academy of Pediatrics (AAP) advises vitamin D supplements for kids who aren’t drinking four cups of milk a day. But the AAP’s iron recommendations state children should be drinking just two to three cups.