2 years old is when you can switch to 2% milk. Still go with the 2% so they still get the fat (for their brains) you can still give full fat yogerts and cheeses if you want, but you can switch those as well.
Also according to the Canadian food guide children (at 2+ years can't remember the age it changes again at the moment) Only need 2 servings of milk a day. Thats the equivolent of 2 cups of milk, either milk its self or milk products.
Its ok if the eat more of course, but you want to make sure that they don't drink to much milk (or juice) that it interfears with their appitite.
My friend just had an issue around this with her son who turned 2 on Nov 2ed and is only 20LB's. He was not eating like he should but was still having 4 8oz cups of milk (as well as 2-3 cups of juice) He was turning into a "milk baby" now she is working towards balencing that out better so he can eat what he needs and gain that wait he needs.
Its all about balence, as is everything in life.