It's a nice thought Ruud, and i appreciate you showing your concern. but as Harry says a petition has to be directed at someone who is in a position to do something. As it stands, there isn't a law anywhere at the moment that says a parent can't allow his child to start up a forum, put himself at risk and also other children.
As Harry says the Observer doesn't usually admit an error. They only tend to do that if they have made a legal cock up, and risk being sued.
Keep watching the paper's letters page and see if they do.
The most we can do through them is send them as many emails and letters as possible, letting them know how strongly we feel about it. Should give them food for thought if nothing else.
Keep watching the paper's letters page and see if they do print anything.
Possibly a couple of people you have spotted on the forum are trying to prove a point?
Look at the posts from a different angle if you go back again.