My wife and I, our son, his wife and our three grandkids, and his wife's parents went to Fun Valley Family RV Resort just west of South Fork, CO every year from the time our youngest granddaughter was a month from being born, and for the next 9 years. Lots of on site activities for kids. Check their web site. We love it and still go back, just DW and I. Son and his family have moved on to beach vacations. A fun place. But many people do not like it for the very reason there are so many families with kids. And it can get quite crowded around July 4th.
In the same area are many rivers and lakes, Creede (old mining town with mining ruins you can visit), Pagosa Springs (hot springs), Wolf Creek Pass (likely still snow on top end of June), Great Sand Dunes (fun in late June when the creek is still flowing across the lower dunes), Cumbres & Toltec Steam railroad (would do that again), float trips down the Rio Grande, and just a beautiful area. And there are other RV parks in the area if the crowds and kids are not your thing.