And as far as putting a kid on a green-to-showing horse and letting them dabble, there's really nothing innately wrong w/that if the horse is sane, like you said. But there is a strong possibility the kid will get discouraged -- been there, done that. If you want your youngun to have fun, and you're not a trainer yourself, then you find a horse who can already perform the job you want done - at whatever level you're wanting it done.
And around here, you're not going to get anywhere "dabbling". I mean -- if you're going to spend the money to go show, it would behoove you to get a horse that would actually give you a way to do that. Case in point. A girl in our area came to me for riding lessons. She started out wanting to jump, but then - like me - she and her family determined it was just easier to go the speed event way. So --- they took one of their own horses who was broke, but not trained for speed events... and she had a miserable time that summer. Horse wouldn't go in the arena, horse didn't know the patterns, horse was an old jumper and knew what a show was, but she was sour and needed some training.
So - mom asked, "Will you train her?" I said, "I will, but let's do this instead..." So she borrowed a horse from me. A horse who could carry her daughter around the patterns safely - either at a walk, or a trot, or at a canter - and accommodate her beginning unsureness, yet had enough speed in reserve to make a decent sort of showing when the youngun got enough confidence.
They played at the shows for a summer and had a great time. MUCH better than the year before. They used her again the next summer and finished well enough in their association to qualify for state events. Mom asked me, paraphrased, "What are the parameters w/in Joy (the mare) will work for M--?"
I answered, "Until she wants to win." I knew my mare's capabilities, and winning in our tough, local competition wasn't part of it. <lol> (We are in Mississippi - folks around here don't play around w/the speed events, they're serious)
So --- at the state show the girl piloted Joy to a personal best time for Joy in all their events. By then Joy was completely maxed out and had gone over and beyond anything I'd ever seen her do, and the girl had learned a lot and was ready for more speed. They bought an old rope horse who didn't know the patterns, but who was broke, broke, broke. The pair won High Point Speed Reserve Champion their first year together.
Now THAT is what I'm talking about. They could have piddled around w/their old jumping show pony, but the girl was super frustrated and wasn't having fun. So, they got a horse who was doing what they wanted the girl to do -- have fun at the shows, get out in the classes, and learn how to run the events. Then when she outgrew that horse's abilities they bought a horse who didn't know much about patterns, but who was willing and fast and by then their daughter had three years of running under her belt and they had an absolute blast at those shows.
To my way of thinking, you can't really compare speed event shows in an area where that is the major sport, to play day/ gymkhana shows in an area where it is more of a novelty. IMHO, and no disrespect intended.