The kids' favorite one from last year was:
Jingle Bells, Batman smells
Robin laid an egg
Batmobile lost a wheel
And the Joker took ballet
They'd have great fun rearranging who did what... Robin would smell, or Joker would lay an egg... lemmetellya, that can make for a real monotonous cross-state trip

Yep, fifty miles of that, with them thinking that each time they sing it, it's hilariously new [img]graemlins/nono.gif[/img]