According to my easy child they can chat with anyone who is playing but the language is screened as it's posted. In looking around it looks like there are also side chatrooms which he's never mentioned nor have I noticed him using. Our computer is in the kitchen so I usually get wind of whatever is going on unless someone sneaks when I'm away.
Here are some parent reviews:
http://www.google.com/search?hl=en&q=runescape+parent+review
I'm a stinker about not letting my kids into this kind of stuff too early--difficult child I expect will be highly addictive when his turn comes.
