I forgot to mention, that out by the interstate on the south side of Springfield, there is Knight Adventure (or Action Park, I can't remember). They have lots of rides for children and you can take in an outdoor drive-in. How's that for a retro thing.

Also, a great place to stay would be at the Route 66 Hotel and Conference Center. This is an actual old Route 66 Hotel, having formerly been a Holiday Inn. As you can imagine, it's all things to do with the road. They have an outdoor pool which is great for relaxing, and what kid doesn't like a swimming pool?

Make sure to try a horseshoe meal while in town. It is a central Illinois tradition.

Keep on Down that Two Lane Highway. --RoadDog