Honestly..... if your kid is on the internet he has most certainly seen much worse than he'll see here. You seem to be keeping an eye on his playing here, maybe you can instruct him in the game some. I don't think most of these other fellas would be slinging stuff his way otherwise.
BTW I think you'll find many more adults and young adults on this game than smaller kids.
With that said we still need to police our language from time to time.