Personally I would have the kids parent take out personal insurance policies for each of them.
This is the reason I gave up teaching martial arts to kids. Instead of giving kids somewhere to go and have something to focus on, i spent most of my time battling red tape and avoiding some pen pushing w@nkers who said i wasn't allowed to do this, not allowed to do that, no assisted stretching, no conditioning exercises, no contact sparring even with full body protection in training for an olympic full contact sport.....
Good luck to you mate.