When a child's body is unable to digest lactose (the sugar in milk), he may experience symptoms ranging from a mild bellyache to crampy, diffuse abdominal pain with gas and diarrhea. To diagnose lactose intolerance, your pediatrician most likely will have you eliminate all lactose-containing foods from your child's diet. This may include avoiding everything from milk to frozen waffles. If this tactic relieves the stomach pain, your doctor will then work with you to figure out a diet that your child can tolerate. Some youngsters are fine as long as they only drink milk with food; others may have to avoid foods with lactose entirely, and get calcium and protein from other sources.