We visited Hidden Valley years ago as a family (my sister and parents). We were later joined by my sister's best friend (and my "other little sister"). We had a great time staying in the rented chalets by the lake. There were plenty of other teens around as well, and we developed long lasting friendships with them as we would hang out by the lake all day and then sit around the camp-fire by night. Perhaps could have a few more organized activities, but this is mainly a do-it-yourself spot, and is a great location if you are visiting Hidden Valley Ski Resort in the winter (which we returned to do!)
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.