Mundo Hot Springs, Cambridge... went there for the eclipse with kids, grand kids, had a great time.
Haven't done too much winter camping and don't know exactly what you are looking for, but that would be my best suggestion off the top of my head.
In the early spring, Bruneau Dunes is our favorite with the kids or without. Usually just a bit warmer than the surrounding valleys and walking the dunes or playing in the sand will keep the younguns busy for hours.
18 Aria 3901-"The Wined Up Bus"
2016 Wrangler JKUR