When you travel by car with children, it is important to plan for high energy activity breaks along the way.
Take along a jump rope, frisbee, balls and/or roller skates, so kids can work off excess energy when you stop at rest areas. (A good strategy for travel with dogs also.)
And plan your trip to include stops at national, state, and local parks and recreation areas along the way. Not only will walking a trail, climbing to a scenic overlook, or visiting a national park visitor's center break up the trip and provide needed rest and recreation, but the family will find it enjoyable to see and experience different parts of the country.
When you are in the car, instead of watching movies or tuning into an electronic game, keep the whole family busy with old-fashioned interactive games like "I Spy (with my little eye)" or the license plate game (how many states can you find?) that will help them to tune into the world that is passing outside the car.