* Don't underestimate what it takes. A bathroom stop with four children (6, 5, 2, and 1) who are all walking, will take at least 20 minutes. Add five minutes for any child that is not yet walking and needs a carrier or a stroller. With the exception of rest areas, most bathrooms will be too small unless you can find a handicapped bathroom. Look for these signs on the road with the restaurants or gas stations. If it's marked handicapped accessible, chances are you will find a bathroom big enough.
* I do not change the diapers in the bathroom. Ever. I always change diapers in the car AFTER the potty break has been accomplished. The babies can wait a few more seconds, but toddler bladders cannot. I also buckle and strap in all the children before changing diapers, only unbuckling the child that needs changing. Try to have a diaper station (with enough room to lay a child down) in an easy to access place. Right now, this is the space in front of David's car seat.
* Toys and DVDs that are brand new (or have been hidden from sight for a few months) go a long way in entertainment value. Since our children watch very, very little TV at home, our in car DVD player is quite a treat. I usually limit it to two DVDs at a stretch, and then I'll encourage some other kind of play. Stickers and felt boards are pretty big in our car, and for the older children, magnet boards. Coloring books, large enough cars that won't be easily dropped, and soft dollys have all made the trip with us. Rotating them and introducing them through out the day after stops keeps things fresh.
* Pillows and blankets make great "walls". Don't pack these in the back- pack them in such a way that they provide division between children. The "Mommy, he looked at me/she touched me" whines will go way down, and it also encourages rest. If you're lucky, older children may fall asleep. Ben and Isaiah also like to use them to make caves and tunnels for their little cars to go through.
*If you are traveling with a non-nursing baby (and honestly, I would not recommend traveling with a nursing or bottle feeding infant alone with other children) do yourself a favor and prepare all the bottles ahead of time and place them in the cooler. Trying to find the water bottle and filling the bottle without getting powder everywhere is an exercise in frustration. Same for toddlers who need sippys. Fix your approximate number in the morning before traveling, enough to last the trip. Trying to find the sippy cup buried in the luggage will drive you nuts.
Most of all?
Relax and have fun. Lower your expectations substantially. If you are stressed out and on edge, the children will play on that. But if you approach it as the great adventure and talk about all the fun you're having (even if you're not) the kids will engage with it and join you. Remember, always travel with a cell phone and check in with somebody every hour or so. Always call someone when you stop, as you are turning the car off, and then again, when you are getting ready to get back on the road. BE safe. A McDonalds in a well populated area in the evening is much safer than a deserted ill-lit rest area.