Actually, this is incorrect. So long as the person reasonably believes the person they are interacting with is at the age of content, they can avoid any charges. Admittedly, I wasn't certain of this myself but googling around I found
several articles. Bear in mind, this is Facebook and actual people involved not avatars in a fantasy world. I can't imagine ERP would go anywhere, legally speaking. Which is rather scary to think about.
Needless to say, this only makes parents being aware of what their children or teenagers are doing that much more important.