I think it is something to be assessed on an individual basis. I have heard that from 2 you should give them low fat dairy, however I have kept Nat on full fat because she doesn't gain weight well (she restricts her diet a lot) and it gives me comfort to have her continue on full fat. This isn't an educated decision I've made though - it just seems right to me. I've made an appt with the dietitian to discuss stuff like this in a couple of weeks so I can probably post a more educated opinion after that, LOL!
I think that once they get to about 2 their fat requirements are less than when they're infants. At this age you'd expect them to have similar requirements to you - the food pyramid shows you only need a small amount of fat, especially saturated fats. You can get healthier fats/oils into them from things like fish. If they're eating a balanced diet then they're probably getting enough fat/energy requirements from other foods so full fat dairy is unnecessary.
I'm pretty sure the recommendation is there to protect kids from diets that are too high in fat - an issue which is becoming more of a problem these days I believe.