Go to the place you want to see most, first.
Pulling a trailer - 300 miles a day on non-sprint days and maybe 2 sprint days where you try for 500-600. I think my record is about 700 miles in a day and it's not fun. Plan to spend 2+ days at the good places rather than trying to do big drives every day.
This kind of trip is a very fine line between an excellent childhood adventure for kids and repressed trauma that lasts a lifetime.
Take it slow, take it easy and let the kids guide how much you sprint.
