Using you post Amanda.
I think when you are young 8-12 YO, if you don't have a parent to teach you a HC may be a good option. What you need is the foundation, good mechanical skills. After that most of whatever they have taught you can be simulated at home. It shouldn't take 100 visits or 4 years of lessons to learn to hit a ball.
There is nothing different hitting at 12 than you will learn at 18. It's repetition, it's skills. All you do is to keep them sharp. Again, proper equipment at home, the time to use them, live batting practice, and real games should be it's own teacher.
Ehhhh... the science has changed a bit since I was 12. No longer are they (most people) teaching "hands up by your ear like a telephone" or "elbow up" My swing at 12... vastly different from my swing at 19. It's a progressive thing, with various tweaks. I used to step, then I didn't take a step, now I'm stepping.
The problem with kids is that they pick up bad habits from places when not with the HC... and the HC has to undo it. There's also the kids who lack the knowledge of their bodies to be able to detect when they are making mistakes.