For our family vacation this year, we all went to Flaming Gorge. Half of the family wimped out and stayed in a hotel, while the rest of us whipped out the tents. It was actually very cold the first night - in the mid 30's, but the second night warmed up to a nice 45.
We took the oldest 3 (Brandon, Daniela, and Ethan) river-rafting down the Green River. They loved getting wet, but especially loved paddling. They splashed dad a few times and thought that was too much fun.