I drew this to demonstrate 3D printing for my kid's 1st grade class. It took all day to print, and I had to cheat a little with the wheels, but the kids enjoyed watching it slowly build. The wheels, if you print them at a high resolution and decent fill, will rotate on the axle on a captive hub.  The axle stub can be glued into the bus body, or something you create.  At lower resolutions and/or with less fill, the axles will break off before the wheel will break free of the hub.  At the necessary resolution for the wheels, the bus will take longer than a school day to print.  Thus, I had some good wheels in my pocket and tossed the ones that I printed in the class. No, I didn't take a picture of the result.