Rent a film projector and use a large screen (the back of a pool or just a strectched out sheet). Make the little cars out of cardboard boxes. Pop in a great kids movie. Serve popcorn and hot dogs and its a great time for all. The kids could even decorate their own cars as part of the party.
Have you heard of the Road to Recovery? It's an American Cancer Society program that pairs volunteer drivers with patients needing transportation to/from treatment. At Relay For Life, we have a Road to Recovery Race. Teams make cars out of cardboard, plastic, wood, etc., big enough for 2 people and race them. Don't miss out! Make a car, decorate it, bring it to Relay, show it off, then race it to win! Want to volunteer to be a Road to Recovery Driver? Call 1-800-227-2345.