Private servers, with whitelists. Because the other players are not anonymous, they're less likely to behave poorly. As the admin, you can ban them, and either call their parents or let your kids deliver the news in person, much as you could if someone came over and started breaking things in person on a play date.
"""
Hi, this is Alice's dad. Mal has been really mean to her when playing on our Minecraft server. It's a shared creative world that Alice, her friends, and cousins have been cooperating to build a city in together. Mal decided it would be fun to destroy most of the city, and cover the rest of it in lava.
This really Alice's feelings, as she and the others have spent a long time building together.
Unless Mal will apologize to Alice and the rest of their friends, we aren't willing to let Mal play with us this way.
"""
There's probably a better way to give the "your kid's being a jerk to my kid" than what I came up with off the top of my head, of course. I suspect that the rest of your kids' peers would swiftly ostracize griefers, as well.
""" Hi, this is Alice's dad. Mal has been really mean to her when playing on our Minecraft server. It's a shared creative world that Alice, her friends, and cousins have been cooperating to build a city in together. Mal decided it would be fun to destroy most of the city, and cover the rest of it in lava.
This really Alice's feelings, as she and the others have spent a long time building together.
Unless Mal will apologize to Alice and the rest of their friends, we aren't willing to let Mal play with us this way. """
There's probably a better way to give the "your kid's being a jerk to my kid" than what I came up with off the top of my head, of course. I suspect that the rest of your kids' peers would swiftly ostracize griefers, as well.