If you really want to get them interested in aviation, pass around copies of the FAR/AIM.
Really though, kids that age love hands-on stuff. They run towards the exhibits in the museums where they can put their little sticky hands on interactive doohickeys. Do you happen to have any yoke/stick/throttle/pedals (maybe a stretch but worth an ask). Like from a sim or similar? So that you can explain how the controls work from the pilot's perspective. (Pull yoke, cows get smaller, push yoke, cows get bigger, etc)