I am super familiar with that area of southern Utah/northern Arizona and there is a TON to do there! I'd recommend staying in Kanab (home of Best Friends Animal Sanctuary, hint hint) as pretty much everything is in about a 90 minute drive in any direction. There are tons of affordable AirBnBs, cheap, clean chain hotels, and tons of campgrounds. From there you could do Zion, Bryce, Canyonlands, Lake Powell, Grand Canyon, Coral Pink Sand Dunes, Grand Staircase, slot canyons, even apply for The Wave (this might be a lot for the little one though). They definitely are NOT all the same! I'd advise going before Memorial Day if you can as it gets really crowded and HOT -- like deadly hot -- in summer. If you're comfortable navigating on your own, you can definitely do so with AWD or 4x4, but you can also take tours with guides to any of these places.
Driving from Vegas is further than it appears. If you can fly into St George reasonably, do so.
A few good guides to the area:
https://www.bestfriendsroadhouse.org/area-attractions
https://www.visitutah.com/articles/...0210&ds_rl=1285028&ds_rl=1290213&gad_source=1
https://www.roadtriplocals.com/blog/best-things-to-do-kanab-utah