I think the difference is really negligible, when you are talking about normal healthy kids I wouldn't bother swapping. We were using low fat here befor Pie came along - we were all older & it was just for coffee & cereal - now we just all have full cream. Tastes nicer too

ETA - Miss E I have heard that too, although not sure if it is a recommendation that you make the change at two, but certainly that before then they should be on full fat products, ITMS?