Milk is an important part of a toddler's diet because it provides calcium and vitamin D, which help build strong bones. Kids under age 2 should drink whole milk for the dietary fats needed for normal growth and brain development. When your child is 2, you can probably make the switch to low-fat or nonfat milk, but talk with your doctor before doing so. http://kidshealth.org/parent/growth/feeding/feed12yr.html