Yes, there is extreme porn easily available on the Internet. No matter what a parent does, when their child reaches the stage of development that they become interested in sex and porn, they will access such material whether the parent permits Internet access at home or not. Many kids these days see their first porn pics and videos on a friend's mobile device at school. OTOH they will already have had a lot of exposure to extreme non-sexual material in everyday TV and films, and so will view it in a similar way - i.e. it is make-believe and nothing like real life. Unless the child has far worse problems, seeing such material will be less harmful to an adolescent than being told the story of Little Red Riding Hood (and other violent fairy stories) was when they were 6.