I commend you for giving your family these experiences. I'm trying to do the same. Mine are both 9, so I'm a few years behind you. We are leaving in June for 42 day trip to the same areas. Just this last week I nailed down the last of our reservations. We're leaving out of Greenville, SC, so a very similar trip to yours.
Here's our itinerary:
-El Malpais
-Petrefied Forest
-Painted Desert
-Sunset Crater
-Walnut Canyon
-Grand Canyon (4 nights)
-Vermillion Cliffs
-Zion (5 nights)
-Bryce
-Capitol Reef
-Arches (3 nights) - off roading
-Mesa Verde
-Durango
-Ouray (4 nights) - off roading
-Black Canyon of the Gunnison
-Pikes Peak
-Home
Hope that gives you some ideas. Enjoy the planning and the trip!