WASHINGTON (Reuters) - President Barack Obama appears in an upcoming Cartoon Network documentary aimed at encouraging bullied children and others to speak up, and says that as the father of two young girls he is deeply concerned about the issue. In an introduction to the 30-minute film, the president appeals to students, parents and teachers to take a stand on bullying. "It's wrong, it's disruptive and we can all prevent it," said Obama, who hosted the first White House conference on bullying last year. He said that he was speaking not only as the president but as a father. ...