www.fantage.com is really cool and I know it is good for 12 year olds because I am a 12 year old!

There are a few.  One of them is www.fantage.com.  It is a really great website made for kids.  Another fun website is www.clubpenguin.com. It is also a really great website made for kids. P.S  And none of the website allow swearing or any other bad things like that.   Hope this helped!