Invest in portable dvd players for each of them or if you have an Ipad, get the digital downloads of thier fave movies.  MP3 Players and headsets that has their favorite music on it.. and for Mom: travel bottles of wine :) 

We leave tomorrow for a week long vacation with a 14 hour drive. We did it in February too. The trip down was good because of excitement, the trip home was hell. My only advice is snacks (lots) and a DVD player.

If your car does not have a dvd player, consider getting a portable one. The price of them is down -- below $100 now.  If the kids have hand held game consoles (ie.. nintendo ds) go to GameStop and get some used games for the trip.  We drove to Orlando from Northern Virginia when our daughter was younger.  She packed books and drawing pad and markers along with the dvd player and her ds.  It is a L-O-N-G trip.  

My 4 yr old does a 2 day trip every 2 months to visit her dad. I think he's insane to drive but he says it works. When she is getting all wound up he stops at a rest stop that has a Park, lets her run for 20 minutes and keeps going. She has an ipod, DVD player, and a handheld leap frog for these trips. But usually she colors with her color wonder markers. Good luck... eventually they will sleep. If not promise them an overnight hotel with a pool and free breakfast.

We leave Thursday for a 10-hour trip with our 7-month-old daughter. She is breastfed still and is very spoiled. Any tips on that?!

We drove to DisneyWorld from Ontario with our three kids a couple years ago... over 24 hour drive broken into two days, with kids who were aged 7, 5, and 2 at the time. My recommendations: DVD player (our van has one... if your car doesn't, it's worth buying!)  Doodle Pads.  Books.  Snacks.  Electronics.  And headphones/books to read in the car for the shift when you're not the one driving... blocking out the kid-noise for a couple of hours between driving shifts helped enormously!

We did a 24 hour drive from alabama to arizona, and then back again a week later. We drove straight through, hubby driving through the night, me taking over in the morning. Dvd player, let them run around at rest stops or when u stop for food. Oh and if someone is feeling carsick, hand them a lollipop. Works like a charm.

We did this trip last August with our 3 kids and my niece. Though we were going for a much sadder reason to see my grandma who was in hospice care. The actual traveling was pretty easy my kids love getting to eat out its a treat for them. The hard part for me was getting my 2 year old to sleep in a hotel room! We learned that its better to check in at dinner time rather than bed time so he had a chance to wind down and get used to the idea of sleeping somwhere othet than his bed.

We do a trip from Oregon to San Diego every year, its about 16.5 hours....I let my husband sleep all day and we leave at about 3/4 in the afternoon and drive straight through, with one stop for dinner. It works out really well when they are sleeping-we tried it once during the day and it was pure hell.