Ryan,
You need to break out the trip planning software. From Lansing (just as a reference):
Yellowstone is 1600mi
Grand Canyon is 2000mi
Between is 900mi
With a coach full of kids, even team driving, 400 miles is a very long day. 500 mile days are a study in survival. Even if you allow the kids nature stops underway (not advised), just food (even when onboard) and fuel stops will cut you down to an average speed of close to 50MPH.
Yes, first time we went to Yellowstone, we did it in 5 days. We later discovered how much we had driven right past. The second time we took 9 days and had a much better time.
If you want the kids to remember the vacation as fun, don't make it a Bonzia run. There is a lot to see in both the northern tier and along the southern route (like Rt66).
You don't even have to look very hard to find interesting things along that much road.
Matt
