6 year old did great. I kept her full with chicken nuggets and smoothies from mcdonalds. We've done a bunch of longer road trips. I try and head out by 7am, but now that I can't carry them both out to the car, our departure time seems to be getting later.
For the car, we had this for pillow and blanket storage. I also had back seat organizers filled with various things (binoculars, digital camera, usb fan, magnetic tangram, sunglasses, summer brain quest workbook 1st grade, drawing pad, color pencils, markers, and crayons)
Highly recommend hitting up the library before you head out. The tv shows are 21 day rentals. The kids watched pokemon and ducktails for hours. We actually survived 2.5 weeks with only 1 ipad!
If this is a 1way trip, you can priority ship them back to the library in a flat rate for under $20. That's a lot of free entertainment(hooray for libraries!!!) for the cost of return shipping.
As for the rest of the trip, I've never stayed in Sante Fe. But when traveling with kids, you have to do the things you want to do:)
In Denver, drive up to the top of Mount Evans.
After Sante Fe (drove thru it once on the way to El paso, so can't add anything... head to the Grand Canyon. In the park is good. The Best Western right oustide the park is good. Under Canvas is spendy and a bit of a drive to the park, but the kids with probably dig it.
Bryce Canyon is under rated and will be way less crowded I would stay there. Or make sure your reservation is refundable and check for cancelations for in the park at zion. The lodge location is amazing.
After Zion, the kids are probably too young to go on a proper tour of Hoover Dam (I'm a Dam fan), but stop at Lake Havasu and Junior Ranger. They have neat stuff to look at.
If you overnight in Las Vegas, go with the Marriot Chateau. Get a 1bedroom. They have a washer/dryer. No casino and the pools are open after 6pm. There's an entrance right across the street to the Planet Hollywood so you can pop over to their mall food court area for the restaurants if you don't want anything from the lobby or if you don't want to cook.
The hotel also has a kid's club (or they did pre covid). They had crafts for a small fee. my kids painted a ceramic bank (under $10) occupied them for at least an hour while I got to sit in a corner a read a book.
If you don't have a Parks Pass yet, go buy one at REI.
I think that get's you to California! Huzzah!!