Although it can cause digestive disruption and discomfort, lactose intolerance will not produce dangerous results, and can be easily controlled through careful diet. Oddly enough, hardly any adults in the world can digest milk sugar after the age of 20. The exceptions are most Caucasians of northern European origin. Although less common, in infants and children it can occur after a severe attack of gastroenteritis, which injures the intestinal wall. But, if you do, give him added calcium gluconate powder, since soy milk does not contain enough calcium.
Lactose intolerance is different than milk allergy.
Avoid all milk and dairy products. This includes ice cream. Lactose is added to many processed foods, including cookies, pancake mixes, breads, canned and powdered soups, flavored coffees, powdered drink mixes, and processed meats. Since you cannot drink milk, eat foods which are rich in calcium. This includes broccoli, dried figs, apricots, blackstrap molasses, and other vegetable greens.