Dairy (milk) is a common childhood food allergy. It is important to read labels when dealing with a dairy allergy; there are many unexpected food items that have dairy as an ingredient, such as some brands of canned tuna. Even some things that are advertised as non-dairy, such as non-dairy creamer, or considered non-dairy for kosher purposes, actually contain traces of dairy. The ingredient label will include even these traces of dairy.  "Whey" and "casein" are some less than obvious dairy ingredients.

The following is a list of some foods to watch out for as they commonly have dairy ingredients.

• Most baked goods
• Butter and margarine (even some types of "artificial" butter
• Yogurt
• Cheese
• Ice Cream
• Chocolate
• Sour Cream
• Cream Cheese
• Whipped Cream
• Cool Whip

There are alternative "milk" products that are available for purchase. They include soy milk, nut milks, rice milk, hemp milk, and oat milk.  For baking, some effective butter substitutes are:  Fleishman's unsalted margarine and Smart Balance light spread.

An important note: Lactose intolerance is different than a dairy allergy. Lactose intolerant people are generally fine with dairy products that have had the lactose removed. However, such products are still dangerous for people with a dairy allergy.

Source: http://foodallergies.about.com