If they weren't there, the kids would keep training without hesitating. Quality instruction also reduces the likelihood of injuries. Sure, at first, you might be a little hesitant, but you get used to it. If a kid was a little worried, I'd tell him to relax and make sure he tells his partner if he feels any pain. So there you have it.
Grappling builds confidence, self-defense skills and motivation.
Your next opponent might just be the jolly old man in the red suit.