D..
They need to be able to run around. Stop at rest areas and let them do that. It's too hard to behave well when cooped up and not able to run off the wiggles. (The wiggles are most of the reason for crazy behavior on a trip!)
Games they can play out loud like I Spy With My Little Eye how many different states' license plates can you find, stuff like that. Bags of manipulatives (not really small pieces that can get lost, though) that you change out so that they don't get too bored. Snacks so that they aren't screaming for food.
Prepare, prepare, prepare before you go. You never know when you might get stuck so that you can't get to a bathroom. For example, my 5 year old had to poop in the worst way, and we were on a turnpike with no pull over (no shoulder at all). Though traffic was moving around 35 miles an hour, it was 5:00 traffic so I wasn't going to get to the exit down the line. This won't happen to you because you most likely won't be on one of these turnpikes, but if there's an accident on an interstate, I could see it happening. My mom was with me, bless her, and she got a plastic bag we had packed and put paper towels in the bottom of it, turned around in her seat and reached back to him, got him out of the carseat, and helped him get his pants down and squat into the bag to poop. She cleaned him with wipies, strapped him back into his seat and closed up the bag. It stank SO bad that she opened her passenger window and strapped it to the side view mirror so that we wouldn't have to smell it.
Being prepared saved us there! However, there are portable potties that make this kind of thing easier - you might look into that. I always kept a few large cups (like from MacDonald's) with the lid so that if we couldn't stop to pee, I could pee in the cup myself (make sure it's a large cup - you can't believe how much your bladder can hold!) and a little tissue. Then you just pour it out next time you stop. That's also helpful for the guys in your family, unless you happen to have one of the urine collectors they have at a hospital (you might be able to find one of those at a medical supply place.)
Stopping to use regular facilities is best, since the kids can run around. But it's important to plan for not having facilities.
Also bring at least 2 gallons of water reserved for emergencies like your car overheating. You need something that can open the lid without burning your husband's hand too. Having AAA is important and have your card with you.
Have a wonderful trip, T.!
Dawn