Francis,
I apologise as I replied, your post hadn't shown up. Nice to hear that you have had good responses. I used to do the same thing with the Navy, we used to take a Sea King to schools up and down the land. Generally it was good fun, the kids always seemed to ask questions that we'd never thought of, which kept the entertainment value up.
Our aim was Navy recruitment though, and we targeted older kids, usually 14+.