Milk — whether it's cow's milk, soy milk, or almond milk — provides between one-fourth and one-third of all the calcium most children and adults should have in a day. Cow's milk is also an excellent source of lean protein. It contains many other essential nutrients, including phosphorus, vitamin D, potassium, niacin, and riboflavin, important for adult and children's health. But you might not know when, how, and why milk should fit into your healthy eating plan. 

Everydayhealth.com says to check this out:

Allergic to Milk? You're Not Alone

Milk is one of the most common allergens among children. Between 1 percent and 7.5 percent of children younger than a year have an allergy to the protein in cow's milk and formulas based on cow's milk. But there are lots of alternatives to cow's milk — soy milk, almond milk, and rice milk, to name a few. Be sure to read the label when choosing alternatives, Crandall says. Some have lots more sugar and fat than cow's milk, and some have less. Many of the milk alternatives are fortified with calcium. She suggests choosing substitutes that provide at least the same amount of nutrition as milk and sticking to unsweetened varieties to scale back on calories and added sugars.