get there when the gates open. the up close tour is the best. we had a great guide and you get closer to the launch pads than the general tour takes you. also the lunch with the astronaut is wonderful. great buffet lunch with beverages (as much as you want) and a great talk given by a nasa astronaut.
you can always check in advance on the ksc website who the astronauts will be . they post a couple of months in advance if not more. we had an astronaut that was on hte back up crew of apollo 13 and also flew the space chuttle. my son loved it.
How old was your son when you went?