Hi! My family drives to Florida every year with our 3 sons (ages 10, 9 and 4). It takes us about 25 hours to get there. I know, I know, we are CRAZY! But it's the only way we can afford to go the Disney every year
My older boys love to read and both own gameboys, so before the trip we buy new books and borrow from the library. We also let them each pick out a new gameboy game for the trip (plus borrow/trade with friends). Then, they are all set for the LONG car trip and are actually very good as long as they don't sit next to each other! (that's another story). Our youngest is the one who needs to be entertained

In the past (and when the older 2 were younger & couldn't read) we always rigged up a small tv and vcr in our van. Works beautifully!! Survivethedrive.com rents them for $99 for 10 days I think. I pack lots and lots of snacks because as long as kids are eating, they are quiet!! Lollipops last a long time - an added plus. Also those candy necklace things are great too. We do pack healthy stuff too in case some of you are wondering

A fun thing to pack in a ziploc is lots of fruitloops and cheerios and a clean shoelace for the little ones to make necklaces with and then eat! I don't pack a lot of drinks because, well, you know.... My little guy naps during the afternoon plus we drive straight through the night. By the time the boys are waking up, we are about to cross over into Florida. I would wake your guys up early early (4:00 a.m.) and they will go back to sleep for the first 2-3 hours, plus your little one will nap again in the afternoon (maybe even your older one!).
Magnadoodles & etch-a-sketch are great for the car, as well as coloring books, maze books, puzzles, etc. Stickers or colorforms are great. Wikki-sticks are great too for the car as they will stick right onto the windows. Talk around with friends and do a "toy swap" before your trip. That way your kids will have "new" toys to play with and it doesn't cost you a cent! We make LOTS of stops on our way down - every 2 hours or so. If you go onto the Mcdonalds website, you can get a printout of all the Mcdonalds with playspaces along the route you will be traveling. These are lifesavers!!! We also try to stop at any malls we see along our route. It is fun to just walk around and the kids usually pick out a new book to read or an inexpensive toy to play with.
Sorry so long winded. Hopefully, you can get some ideas from this website. Have a GREAT trip!
Kimberly