Some thoughts on "having fun".
First off, you have to understand one thing, that phrase "having fun" means 100 different things to 100 different people. Winning trophies is "having fun" to some, maybe most. For me, "having fun" was all the things I did before the race in preparation for my "having fun" attempt to win a trophy. The trophy was just a symbol that while "having fun" I did everything "right enough" to be the best at that particular race. All that effort, leading up to that race, and the win/trophy of course, was all part of my "having fun". In the beginning, just learning how to drive the kart faster was "having fun". The key be in that, just driving the kart was one thing, fun enough for some, but learning how to drive the kart faster each time I went to the track, was, for me anyway, more "having fun".
Just driving the kart is fun too, but all my effort in trying to make the kart faster, was more fun. In my heyday, my first thought on waking in the morning was how to go faster. My last thought before drifting off to sleep at night, was how to go faster. That was fun for me.
Now I've never had a five-year-old driving a kart, so I can't say that I understand what they're going through, but I understand, as a builder/mechanic, what the adult is going through. Or should be going through, in my humble opinion of course.
I once build a go kart for my wife to drive, and I could hardly control my enthusiasm when she was on the track. I had to make a conscious effort to control myself. Not easy! Not exactly the same thing, but as close as I've ever been to what you're going to be going through.
While attempting to teach her how to drive, I discovered a question was much better than a statement.