I just did this exact same trip along the I-40 and Route 66. Our goal was to make it to the midway point of Rte 66 in Adrian, and we did. Feel free to PM me any specific questions. I will say that what really came in handy was a full compliment of over the counter medicines as I ended up getting a stomach flu on the last leg of the return drive and my wife came through with having everything I needed in the middle of the night. She also drove us home from there as I was in no shape to do so. I know that's oddly specific but damn it made a huge difference.

To see the grand canyon, get there early, like at 7am to minimize heat and traffic/large crowds and wait times to get in. Make time to also stop at the petrified forest national park...totally worth it.

Let me know what cities you want to stop at or what kind of activities you like. We saw so much stuff, mostly off the beaten path kind of stuff that was amazing.

Oh yeah, for an awesome Route 66 experience, bypass the I-40 at Kingman and take Route 66 to Seligman and then hook back up to to get to Williams. Don't forget to stop at the Grand Canyon Caverns before Seligman. It is a fun experience.

What are the ages of the kids? I traveled with my wife and 8 year old daughter. She's been conditioned for long roadtrips, but a nintendo switch, a tablet with loaded movies, and coloring books help.