Excellent idea Kate, I've setup a Juniors forum in the Community section. Only registered users can access it so casual visitors to the forums won't see it. That means we need word of mouth to get it going, so please encourage any youngsters you know who might be interested to register.
As for keeping it safe, the forums are carefully moderated, and we get notification of all new members and I then check them out.
If anyone wants to volunteer to help moderate a particular forum let me know - you get to wield the editorial pen (not that you lot need it!) and are charged with keeping it interesting if the posts start to dry up.
Dan