If you do end up driving to Las Vegas, coming west on I-40 from Albuquerque, Stop at the Hoover Dam Lodge on US 93. It is about 2 miles from Hoover Dam which your kids will be more thrilled with than Las Vegas. Depending on what time of day you get there, you can see the dam in the afternoon before checking in or in the morning after checking out. Be sure to also take the paved trail to get on the walkway on the big bridge above the dam. The state line and the apex of the bridge are marked on the walkway.
In Flagstaff you might want to visit the Lowell Observatory up on Mars Hill. Since Seligman has been mentioned - the correct pronunciation is se LIG man.

Hoover Dam is Friggin Hot by the way. Another reason it may not be that interesting to the teens.

I'd rather stop in Death Valley, TBH.

Once you have your itinerary locations planned out, have your kids join in the vacation planning by looking at places they want to visit. We used to have our kids do that research with us. We told them if they chose a place that would work with the itinerary; we would try to accommodate it. If they didn’t chose anything, then they couldn’t complain.

Waze is a great app if you are worried about driving state side!

Holy cow! You’ve gotten so many fabulous suggestions. The U.S. is a huge and incredibly varied place. Better to choose a few key places or experiences you’re keen on than try fitting in too much.

Driving laws are are generally similar in each state. Mind the speed limit signs in miles per hour. There’s a kind of unofficial allowance of up to five mph over the posted limit, probably because the devices used to catch speeders aren’t more accurate.

Gardyloo loving your itinerary, have copied it as we may use it in the near future.

I'm definitely using some of these suggestions this summer!