I had an AWFUL experience about a month ago; I took my second grandsons to karate class when the new baby came; we got there early because I wasn't sure how to get there and the boys were playing with a ball, just rolling it between them on the floor.
It wasn't long before some other parents showed up with their kids and let them completely run wild while they were on their cellphones; one of the little bullies took the ball away from my kids and sort of played "keep away" from them, actually taunting them, while their mothers stared in the opposite directions.
I wasn't sure what I, as the grandmother, should do (I think you know what I would have done...LOL) because I didn't know for sure if they were friends of my stepdaughters or not -- and (believe it or not) I didn't want to make a scene in front of MY kids) -- I just wasn't sure of the "social dynamics," you know?
Shortly before class, the oldest one developed a "stomach ache" and didn't want to go into class; I decided not to make a big deal out of it and we just went grocery shopping.
It was a weird feeling for ME not to jump somebody, but I just wasn't sure how to handle it.
that would be weird, i can see why you were afraid to jump these people that might turn out to be your stepdaughter's friends, but my inclination would be to do just what you were wanting to do, and tell the little snots to leave your grandbabies alone!
Hmmmmmm
Sounds like the dojo is a dud. Where my boys go, courtesy and respect are emphasized as much as the physical work. The older boys are taught to look out for the smaller ones as well.