When I stared to train young riders I always started them off tackles! It’s a great way for the rider to develop balance not to mention confidence, but it helps the horse as well... it teaches the rider to not rely on the reins and that’s a problem nowadays because if you rely on the reins you rely on the horses mouth and that’s not good at all. But it is extremely fun and kids have fun doing it.
Coaching! It'll be easier to relate to plus you can go into extream detail with out confusing the class you are presenting to. You can explain about all things you have to look for and the challenges a coach faces in finding ways to explain what to do. Also how you are not just coaching the rider but you coach the horse through the rider. You can go into different coaching styles for different riders and disaplines. Hope this gives you somewhere to start!