Milk Alternatives. There are several milk alternatives, the most popular of which is soy milk. Additionally there is almond, rice, coconut, and hemp based milks as well. You should avoid sheep or goat milk because there is a high rate of cross-reactivity with cow milk.
Milk Allergy. Soy milk, almond silk milk, and rice milk. Don't use goats milk, very high similarity between cow and goat milk with a 92% chance of similar reaction.
Water. The only drink for which the human body was designed is pure water. Milk is for cows to give to their calves until they can eat grass. It is not a health drink for humans.
Many alternatives. Bovine milk is a simple way for kids to get the calcium they need for strong bones. If allergic, soy milk or almond milk are acceptable alternatives. If the kid can get feta (goat)cheese or other calcium sources, there as no need for a milk like product.