THE SITE IS GREAT. IT COULD HAVE ANYTHING BEAD AND ANYTHING GOOD. EVEN I HAVE A NING SITE THAT'S GOOD FOR 10 YEAR OLDS AND UP. SEARCH FOR EZRA'S HUGE REVIEWS ON NING AND YOU'LL FIND IT.
My friend created a site on there (I am also part of her staff), and we have a lot of fun connecting on there. You can post whatever you want on your own site, so it may be inappropriate if there are people you aren't comfortable with.
If you create a site on there you can have a setting so you have to get an invite from one of the members to join.