How young are they? Do they know how to enable the internet? You could just shut down the internet connection.
Well the youngest are 6 and 10. I'm pretty sure they couldn't enable the internet but no one else in the house would be able to figure out how to turn it back on if I disabled it.
Disconnect the internet.
I just want to block them from joining servers in blockland when I'm not there to watch them, if I did that they wouldn't be able to do anything else that doesn't need supervision.
What part of online is it you dont want them using?
Just the join server function.
I think I will just remove the Join Server button like Peaceful War said and, just keep a non-edited version on my zip-drive. I appreciate everybody's help though.