Wow! You really did the park justice with all those amazing activities. We spent two days there a couple years ago, and also found it so much more exciting that we were expecting. The Junior Ranger program was a huge hit for our gang. We did get to swim in Boiling River, which was an amazing experience. Too bad you missed it, though you had a full trip.
We also hiked to Yellowstone Canyon, which is spectacular! It is really colourful, has some beautiful waterfalls, and is easier to take in than the Grand Canyon, being that much smaller.