Certainly when I worked in the NHS we saw children in out patients after this type of injury, whether we saw them all or just those who were problematic i am not sure. I know from collegues that cut backs are effecting services.

Definitely ask about it when you get the cast off. Even just getting some advice is useful. Children do generally just get on with it...however knowing what to watch out for is useful. Even if you have to see a physio privately (who deals with children) for advice it is probably worth it (do check out whether they are registered with OCPPP (private physio organisation) this site will give you an idea of their specialities, also ask about experience levels etc. Generally if a physio is registered with BUPA for example they will need to be at least 5 years qualified.

Having a 3 year old and 5/12 old I know how much mischeif they can get into and how you ant to do your best by them. If you are doing activities with your child to help mobilise / strengthen make sure that they are fun, varied and for short periods only.

Good luck and do ask about seeing a physio.