Riding lessons for younger kids

And they will be able to prove liability because you don't know what you're doing as an instructor, they're on your horse, and you're claiming to teach. You're still at school so presumably a minor which means they'd go after your parents assets too. And since you clearly don't know how to teach beginner children there's a good chance that what you do teach them will have to be unlearned if they want to ride properly in the future.

For everyone's sake stop this. Once you have a riding instructor qualification and insurance then you can teach, until then tell the parents to send their kids to a proper school.
If you are in USA, the insurance requirements can be stricter than in the UK. I rode my USA friend's horse with her in the pasture and on my own only in a round pen, wearing a helmet and bp and covered by my own insurance. No money was paid.
However whebn paying, an adult rider can judge whether or not a trail ride horse is safe for them to ride. I once turned down a horse in Texas and was allotted another. A child might not be able to assess a horse. Or might fear missing out on any ride unless they accepted the horse they were given.

Both in the UK and the US customers have to sign a disclaimer before riding. But if the owner of the horse can be alleged to have mis described the horse or to have been negligent, the owner still has liability.