If you're mad, we must be completely insane . We are planning on driving over to WA in September, so we'll be going over the Nullabor on the way there and on the way back with THREE kids, eek! I Googled the other day and found some sites that had some ideas on how to entertain kids on long car trips. I'll copy and paste for you:

For Babies and Toddlers
Sometimes the simplest - and least expensive-- things can delight a baby (at least for a few minutes.) Such as a couple of pieces of mega-blocks that she can try to piece together. Or a few magnetic stick-together blocks. Or a safe little plastic mirror.

Simple, inexpensive, and easy to bring along:
bubbles (use them on stops)
balls (for rest areas during car trips)
nested containers, and objects to put into them

Kids Fun Stuff - Pre-Schoolers
This is a great age for picture books, stickers and activity books, pop-up books, and other low-tech toys and books you can go out and buy, sometimes available low-cost at a dollar store.

Pre-schoolers can also be amused by simple things from home:
masking tape - kids have fun just ticking it, unsticking it, etc.
post-it notes
paper punch
wrapped up presents, or snacks - triple-wrapped; the unwrapping is the fun part
metal tray, and magnets
learn a long story and tell it well: kids like to hear the same story over and over
We also just bought a DVD player with two screens for the back of the headrests for the kids. I really don't know if we will get through it unscathed, but it will definitely be an adventure! We are doing a 6 week trip, so we might bump into you on the Nullabor LOL!

Good luck