Some Light Reading for You
Welcome aboard the RoadTrip America Forums!
I took my two young grandsons to Legoland a couple of years ago and they loved it. While in the area the other great place to go is Balboa Park in San Diego, with botanical gardens, great walks and at least 3 museums with a special appeal to young boys: Auto, Aviation, and Natural History (dinos and giant bugs). I don't know much about biking in Southern California, but I bet these people do. And here are a few places to let your son blow off some steam on the way down.
AZBuck