Too many sources to cite, but calcium is fat-soluable and as adults we store this and vitamins such as A, D, K and E in our fatty tissue and many of us have high levels of these.
Children, being more active and needing more energy to process their food, need more fat for brain development and for absorption of fat-soluble vitamins and minerals.
As has been mentioned, the advice is that you CAN give your child semi- from 2 but skimmed isn't advised as routine until after 5. However, if your child is active and not already very overweight for their age and height, then full-fat is fine.
So...once again, it comes down to the needs of YOUR child. Which is what we've known in our hearts all along (without the government telling us, shhhhh ).
Tricky in nursery with so many children, though.