How is this allowed?

[CNitsah]

Isn't it the case that the clause "protect children from access to age-inappropriate content introduced by other players" is legally covered by the ToS prohibition of third party tools.

I can't think of any player-driven content that would be age-inappropriate if it is viewed vanilla.

That's a good point, but questionnable when you see how unwilling SE is about doing anything about that. I guess there is no telling without an actual trial.

That said, text only can be innapropriate enough. When you advertise your PF as 18+ you know people will use the chat for unsafe things. Sexting is a thing, it's only words, would you say it's safe for childrent because there is no visual support?