I used to fish Yellowstone a lot over 20 years ago. My best friend "Fish Man" (now fishing with God) and I use to fish there 10 days straight every fall. What I remember is license was cheap and there were certain stream sections for kids.
I've fished a lot over the last 45 years for many species in many locations. Yellowstone was my favorite. I often think of the great fishing I did with "Fish Man'. Never before, or again, did I find that catching so many fish could become boring. First hole, second valley, Lamar River, don't get better than that.
Now if I can only spend less time fishing Canada and Gulf Coast, I'd be fishing the many streams in the park.