I gather you meant to say a 24 hour drive, rather then a 4 hour drive.
We are also driving to FLA WDW and are leaving March 31, 2005 from the Toronto area.
I would suggest TV's for the kids with individual head sets. My older daughter has a game boy, TV with all her DVD's on a copied discs, books, colouring activities, a journal, homework etc, sticker activities, and a leap pad. We are leaving early in the a.m. 3:00 and some of the driving will therefore be done while they are sleeping.
we also take kids music on cd's and have the XM radio system for uninterupted music. The kids love to sing along to their music and my DH does not mind this. He also got me my own TV so I can catch up on my soaps that he had taped on a DVD for me - I am behind something like 30 episodes on Days of our Lives LOL and hope to catch up on this as well.
There are some trip activity pages on the Transportation site and we have a book of car games to play on the road.
This will hopefully keep them occupied. If not there's always Gravol which will help them sleep - just kidding I wouldn't use it for that purpose but my older one has on occasion had motion sickness so I will be giving it to her, the fact that it makes her drowsy is a beneficial side effect when driving long distances.
Have fun
Tink&Cinderella