When we do a road trip it is with 4 kids and 2-3 adults, depends on hubby and if he goes or not. My friend and I stop every 2-3 hours. The kids get out and run amok. They need to move around to work out soreness and to get their bodies moving. It will decrease your stress levels too. We stop at places like McDonalds with indoor playgrounds, if you don't like the food then plan on a mid afternoon stop there and eat parfaits. We stop at elementary schools in the evenings if it is summer and still light, or if it's break then any time of the day. The benefit of a school is that it is usually kid friendly, has a fence, is quiet, kids are familiar with rules at school so they act better, etc...if you know of a great park that will work as well too.
We get up, eat a huge breakfast, get on the road.
Stop in about 2 hours for BM's and play time, plus a snack.
Stop in about 3 hours for lunch and play time.
Stop in about 2 hours, some may be asleep and you can drive like crazy until they start waking up and needing to go pee and play and eat. This play time is important, it's about half time in the day and they really really need to get all the play time in they can.
Stop for dinner when you start getting hungry. They need to eat and they will need to play but it may not be as energetic as before, they are starting to feel the effects of the sitting in one position, the stiffening of the muscles, the tension in their necks, etc...they are going to possibly be very cranky and whiny.
Depending on what their normal time for bed is, after they play for a while you may want to get them ready for bed before traveling any further. You can get them in comfortable clothes, sweat pants, tees, pull ups, brush teeth if you want, etc...if they fall asleep you can travel well into the night before stopping again. If they don't fall asleep they will need a late night snack and possibly a bit more play time.
It is so easy to travel in the early morning and after dinner. Miles and miles can be covered. If they are asleep drive drive drive, then stop and take time for them when they are awake.
Our trips are mostly enjoyable, the times when we need to stop and the other mom doesn't really want to are the times when the kids are nit picking and arguing, every little thing is a crisis.
Changing the seating after breaks can be fun too. If the kids are up for it and want to. It may be that they do not want to sit by X due to not wanting to hear their music or be annoyed by them.
Have fun, I enjoy road trips a lot.
PS, Another option I like even better is to wait until evening to start the trip. I love to drive at night, it's cooler, quieter, less traffic, etc...we will get in the car after dinner, a late dinner actually, kids ready for bed. Pillows, blankets, loveys, quiet movies and music on the MP3 players, nothing to get them all stirred up. Then head out. If they aren't asleep within an hour stop for a bathroom break and perhaps a late snack. I keep the kids in the car if they are at all calm. I drive until I can't drive anymore and the other driver will often take over then. We keep traveling until the kid wake up and we need to move around too. Works like any other travel day except you got a lot of miles under the belt.
At this point you can choose 2 ways to continue.
1. stop for several hours, kids can swim, play, eat, nap, etc...while the driver that drove all night rests. At some point during the day it's back in the car and on the way again.
2. get back in the car with one adult sleeping, another adult driving, and the kids staying on the stop, eat, play schedule. Continue as long as possible. You can make your trip in 2 days this way.
Traveling at night is so much easier. I start staying up all night a couple of weeks ahead of time so my body is ready and not going to fall asleep. It is my favorite time of the day when we do this. Sometimes if there are 3 adults one can stay up for a while and they can just visit.