just out of curiosity, how was your hand low enough for her to get it, and the lighter, with her front hoof? were you sitting on the ground?, or was your hand hanging down by your side? But then, it wouldn't have come close to your face. Sorry, just trying to visualize this.
Many horses can never be 100% trusted. it will be good for your kids to learn the basic rules of safety to deal with these horses, as if they were the dangerous ones, not the mellow kind, because they certainly can become dangerous , fast!
I have no idea what caused the kick, but would guess that she was actually kicking out at the other horse, and you just happended to be between the two? Could this explain it?