During the cool summer nights, just around the corner from the Sheraton, there is a large area for concerts. Be sure and check the schedule for what band is playing and at what time. The concerts are free and its a great place for the adults and the kids to hang out.
Of course there are other activities like water rafting and fly fishing. For the former, it will require that you rent a car and drive to a drop off point. You can get more information about fly fishing here.
You won't need a great deal of time here. The high altitude and vigorous hikes really can take a lot out of you. We recommend 4 or 5 days here. It is plenty.