Not knowing what to expect on a road trip can be stressful for a kid. Have your entire family sit down together with a map (digital or paper) and plot out your route. There are lots of these services available online. AAA's free Internet TripTik Travel Planner is a solid choice, and members can get a physical TripTik, a detailed flip chart that takes you through every step of your journey. Let each family member decide at least one thing to do along the way. Once you're on the road, let your kids track your progress with travel and map apps.
Stop. Stop. Stop. And then stop.
Nothing ruins a road trip like grown-ups who drive like they're training for the Dakar Rally. So instead of treating your vacation like it's a way to blast from point A to point B, make getting there part of the experience, and schedule plenty of time to take breaks and see the sights.
For trips where you are driving a long distance to a place where you'll spend several days, a good rule of thumb is to split drive time and out-of-car activities 60/40, not counting sleeping or eating breakfast. We've found that this ratio allows for plenty of time to take in experiences that are more meaningful than a bathroom stop at the 7-Eleven but also get us where we need to go. (Keep in mind that a GPS won't factor in time-sucks like Friday afternoon rush hour in Chicago, or even Cleveland.)
If you're going on a classic road trip in which the journey is the destination, then you need to lower that ratio to 50/50 — or further — to give your family enough time to check out the places you've planned to see and the sites that unexpectedly call to you, from a diner in Pittsburgh to a snorkeling excursion in Key Largo.