It's about a 20 hour drive.
Stop at places like McDonald's with Playlands to eat or snack, so the kids can play off some steam.
About every 2 hours, stop somewhere to get out of the car and stretch your legs.
Pack each kid a seperate backpack filled with things like little toys, crayons, coloring books, a blank notebook, books, pipe cleaners, etc.
Maybe surprise the kids with a couple new DVD's along the way.
Travel with a pair of slip on shoes/sandals. When you're on the road, everyone can slip them off for comfort and when you make those quick stops, everyone can just slip them on and jump out.
Little pillows and throw blankets can be life savers when Dad is too hot and everyone else is chilled.
Don't allow yourselves to continue driving if the driver is too tired. It's about like driving drunk and it's just not worth the risk of an accident.