I suppose technically it's not impossible. I forget how the shell output is wired up... it may even be easy.
As a parent, I don't let my kids play online games with chat. It has nothing to do with the language used and everything to do with the predators that might be out there. That stuff can't be filtered.
...and on the other hand, my kids are so far raised to be uncomfortable around the language that I might want to filter. It's nice because right now it self-polices things like youtube videos and such.
If you want to get into the really super kid friendly stuff, a white-list chat filter would work best... but building up the database is a pain.