There's a lot of viewing to do at the KSC but more hands-on activities and simulators at the AHOF. Space Camp trainers are there too, so I assume your child would enjoy it more.
Rush to the KSC if there's a scheduled launch (just to get closer to launch pad although you can see the shuttles from anywhere), but you can even wander around several areas without paying and it isn't too far from AHOF anyhow.
Wanda