We also stayed at Jellystone several years back when kids were little. It was the only one we could find with a pool. We stayed in cabins because my parents were with us and they don't camp. But we did notice some noisy large groups of what looked like 18-22 yr olds that were partying it up. My husband and I both stated we were glad we weren't in a tent on that trip.
If we go back we'll stay at the park's campground even without them having a pool. But I will add that we are partial to the park campground and generally not as fond of the private campgrounds.