This is actually interesting. The American Association of Pediatrics recommends transitioning kids over to skim milk at age 2. This is because they are trying to fight the obesity epidemic. See recent publications on their HALF inititive: http://www.aap.org/en-us/advocacy-and-policy/aap-health-init...

As you can imagine, this has caused some controversy in the pediatrics world. The pediatrician we go to still recommends whole or 2% milk for our toddler. She actually makes a point to tell us any time her recommendations conflict with the official AAP recommendations and why, which I think is a really nice thing for a doctor to do.