Camping is a great idea, you can rent a small to medium sized RV or you could stay in a cabin. That way you wouldn’t need a tent or the “typical” camping stuff. Here’s a link to some cabin ideas in Yosemite Pines that might fit the bill. I haven’t checked out the site to see what the availability is during your time frame, though. And here’s another site for Camp Curry at Yosemite. And here’s a site for Housekeeping Camp at Yosemite.
Also there’s usually hotels and motels near a lot of the great “camping” areas (maybe Grand Canyon, Mt. Rushmore, Yellowstone) so again you wouldn’t necessarily need to get camping gear, maybe just some day-hike stuff like backpacks and food/water carrying stuff, hiking boots.
I’d like to throw in the idea of an historic vacation to Washington D.C. too. I’ve never been there, but my family has and they said it was marvelous seeing the mall, and the memorials and the White House and the Constitution and the Declaration of Independence.
And another idea is to go to Palm Springs (stay in a motel) and go hiking in the desert at the Indian Canyons and then take the Palm Springs Aerial Tram to the top of Mt. San Jacinto (where there may or may not be snow, but it’s beautiful either way) Here’s a link to the Tram The ride up the tram is one of the most spectacular trips I’ve ever been on. They have new, Swiss made tram cars that rotate slowly 360 degrees while you travel up the side of the mountain. And you travel (in ten minutes time) through about 4 different climate zones on your way up from desert to alpine forest. There is lots of intersting history to learn about the native Americans that first populated the area and tons of very cool information about the building of the tram-line. And there’s lots of kid-friendly places to eat in Palm Springs like Tyler’s Burgers, Ruby’s Diner, Matchbox Pizza, Elmer’s and lots of great Mexican food.
And last, but not least, you could rent a houseboat on Lake Mead or Lake Powell or any other lake where they have them. You can check that out here although I have no idea what the prices are like. You might get a better rate if you were bringing along some other folks, but I’m not sure.