Our son has a severe dairy allergy, and the dietician says 2 extra strength Tums (1000 mg, or 300 mg elemental calcium) are sufficient for a child 4-5 yrs old. They must be given morning and night, as your body can only absorb so much calcium at one time. Our pharmacist says that Tums do not interfere with the absorption of CAH meds, so you don't have to worry about giving the CAH meds and Tums together. And, like Lynn said, your body will "get rid" of any excess calcium, so you don't really have to worry about giving too much. I would caution, however, NOT to substitute any other antacid - especially Rolaids!! - as many of them contain aluminum, which can be harmful to children or pregnant women.