Let the kids have a say.
Kids tend to whine and complain about things that are forced on them, like lima beans -- or long car rides. But if you get your children vested in your trip ahead of time, it should lessen the likelihood that they'll revolt. So carve a few days out of your itinerary, or maybe a few hours each day, and hand them over to the kids.
For younger children, a few hours work fine. During their time in charge, let them dictate when and where you stop and for how long. This might mean stopping at each and every one of the next five waysides, but it'll be worth it if they're quiet during the time in between. Let them determine what you do during their hours, too. Maybe one stop will be to see a roadside attraction, another to get a milkshake at a diner. Older kids can map out an entire day, selecting the driving route and planning all the stops and activities. Suggest they adopt a theme for the day or create music playlist you'll listen to as you drive [source: Hatch].