Is this your first long trip with the kids?
We just got back last night from our fourth big car trip with our son, now 20 months. Other trips done when he was 6 months, 1 year and 18 months. Also, one flying trip at 15 months.
If your oldest likes pushing buttons and looking at graphics, I would really go with the game boy. I was actually thinking about getting one - or something similiar - for our son on car trips, as he loves buttons, lights and noise. It doesn't really matter if he doesn't understand the principle behind such a toy, just as long as it keeps his attention! Also, while my son never watches tv at home, I wouldn't think anything about letting him watch a bunch of videos during a long trip - a bit isn't going to spoil them. My only criteria for a car trip is everyone getting to the final destination sane! If that means video games, tv and 'junk' food, then so be it.
One thing that was a winner for us this trip - little boxes of raisins. My son would pick one out at a time, then munch away. I also had some little disposable cups (dixie?) along and he loved putting the raisins from the box into the cup and back and forth. I also do up little bags of pretzels, crackers and grapes.
The board books that have buttons that play a melody (words to different songs in the book - different button to push per page/song) are a major hit with my son.
Also, a MagnaDoodle --- okay, my son is too young for this and I wouldn't let him play with it unless I was right there supervising him. (I sit in the back seat with him.) But he loves it and it keeps him occupied for hours. We have the smaller MagnaDoodle, which only cost $4-5 at Target. My 3 year old nephew loved this, too, while we were on vacation.
Fisher-Price has a new line of add-on toys around $4.99 each - I bought the helicopter for our trip and it went over good.
Flash cards, though my son loves to look at pictures - but these will keep him happy for a long time. Mr. Potato Head.
One thing that I have done --- I make up one big bag of toys that I can pull out of, then I make up 2-3 smaller bags or even little toy buckets - have them filled up with odds and ends type stuff. One of the bags had a used gift card in it with a hologram picture on the front, a toy car, old cell phone, set of old keys, etc. Just real odd stuff. My son will pull out this stuff and play with it for a long time. Your four year old may be too old to get much excitement out of that and I am not sure about 2 year olds - just reaching that point!
On our way back from Memphis this summer, I picked up a magnetic puzzle/wooden book (age 2+). Son enjoyed that, though it had a few too many pieces on it to keep together.
When we traveled when my son was younger, I was really surprised at how often we had to stop so I could nurse him. I had planned on nursing him while we ate, to save time, but it never worked out that way. Also, Cracker Barrel is a wonderful place to stop and rest. I am not much on their food, but they have a great area to sit, let the kids run some (outside on their patio), clean bathrooms, etc.
Good luck! ~ Suzie

Geogenius makes a map of the US that will tellyou the state names, capitols and other facts when you touch the "pen" to the state. My children love this. By the time my son was 5 he could identify all of the states,capitols, state birds, etc. They also make several others that deal with things like the solar system, dinosaurs, undersea and US presidents. I think they are about $25 each but are very entertaining and educational. KB Toys and Toys R Us should have them.

I agree with the above poster about watching as much TV as they want on trips. It makes for a very pleasant trip.I once traveled from Colorado to south Mississippi (25 hours of driving each way) by myself with a 2y/o and a 3y/o. Blues Clues kept me sane!

Also, I found McDonald's with playlands to be a great place to stop. I ate while the kids played and burned off energy and then I got them some food to eat in the car. I always stay at motels with indoor pools and let them swim for a few hours at the end of the day. I find it easier to get started about 4 or 5 in the morning so that the kids will sleep for a few hours in the car when we first get started. My kids are great travelers and we do it a lot. We only use the TV for long trips (over 6 hours). On shorter trips they sleep, read books or play games.

This geogenius product sounds great. I can't seem to find it anywhere though. Can you provide me a link to a picture of one so I at least know what I'm looking for?
Ginger

I couldn't find the exact US map that we have, but I found one similar. The www.imaginarium.com site has the solar system, dinosaurs and a US map. Just type "Scholastic" in the search and scroll down to see pics of them. Click them for a closer pic and description. The "I Spy" series of books would be good for occupying the time of the 4 year old (and adults, also).

We just got back from a 1500 mile, week long round trip. I'm also one of the the if they are happy, then let them do it people. DH bought them a VCR back in March, it has been worth it. We've been on 4 long trips since then, we haven't had much fussing. The videos the kids watch can be as educational as you want. My kids do well with sing-a-long songs and Thomas videos. DH even taped Blues Clues, Wiggles, Dora, etc. so we wouldn't have to change tapes as often.

I also bring along some kid cds so we can all sing together.

For toys, we brought along favorite cars, trains, and telephones. I only brought enought to fill one backpack. Otherwise, I felt we would be looking for toys all over the place and losing some. The kids got a break from those toys when we visited other people. I quit bringing books on trips because I always get car sick and I'm afraid the kids will be the same.

My 3 yo is into ham and cheese sandwiches right now so I just brought sliced ham, cheese and bread so he had something to eat when he refused to eat what everyone else was having. We had crackers, juice in a box, bananas, apples, and cut grapes for healthy snacks. I got the idea for putting a hole in a container of yogurt and sticking a straw in off of one of these forums. My kids think it is really neat and will eat that for a snack or breakfast sometimes. We ake plenty of less healthy snacks too. The little "Smiles" that are like fruit rollups or gummy bears keep the kids quiet sometimes.

The kids seem to like to sit next to each other rather than apart. We stuck both car seats in the back seat and named it the airplane seat. The kids like to keep us busy busy pointing out trains, windmills, pumpjacks, airplanes, etc.

I know you probably already do a lot of this stuff, but maybe we do something a little different and that'll give you a new idea.

One suggestion I have right away...NIX the crayons. Crayons melt in the heat, and are impossible to get off the car seats (I know from experience)! Get washable markers or colored pencils.

Watch the salty foods. Salt equals thirsty, thirsty equals more potty breaks. Chocolate melts (even M&M's)so be careful with that.

Vickey-MN

And make sure you travel with a little fold up potty, a godesend for us a couple of times when the bathrooms were nasty and freaked out the kids. We do a lot of long trips with our 6yr, 4yr, 2yr, and 6 month olds. I say, let them watch as much tv as they want. Try the gameboy-- you may want to borrow one first in case he does not like it. You have gotten great suggestions here! Plan on stopping to nurse about ten times more than you would think. Maybe you'll get lucky, though.....