Since your son is not drinking milk or eating dairy foods, be sure you include other protein rich foods in his diet. Some meat or fish, or legume grain combinations are good. Also include eggs and nut butters. Having your son drink water for thirst is great habit to cultivate. However, serving more juice than 4 to 6 ounces a day is not.
Most juices offer nothing more than calories.
Choose one that is vitamin C rich. Beyond what he needs to get his vitamin C, juice will fill him up for more important foods. However, if you are serving nutrient rich juices like fresh squeezed orange juice, carrot juice, or other home made juices than you may use some of them in place of other fruits and vegetables. In sum, switch from Tums to a child designed vitamin supplement containing calcium and vitamin D, add a fortified soy beverage, limit juice to 6 or less ounces, and include calcium rich and protein rich foods in his diet. These steps will help insure your son grows up with strong and healthy bones.