While watching a Christmas movie, I got the idea to make my own fanciful push car. This is delightfully noisy when pushed.
http://youtu.be/nQULNy1nBbg
My wife created a model with clay and I scanned it with a MakerBot scanner. Using TinkerCad, I cut a hole in the bottom of the scanned object to accept the wheels and carriage I designed. The wheels snap into the carriage and the carriage snaps into the car. The car was painted after being printed.