YouTube says it is "very sorry" after more disturbing videos were found on the YouTube Kids app. Newsround found several videos not suitable for children, including one showing how to sharpen knives. Another had characters from children's cartoon Paw Patrol on a burning plane. YouTube has been criticised for using algorithms rather than human curators to decide what appears on YouTube Kids. In 2015, two child safety groups complained after disturbing videos were found on the YouTube Kids app. YouTube said it needed to "do more" to tackle inappropriate videos being seen by children. Newsround had arranged for five children to meet Google's Katie O'Donovan. They spoke about distressing videos they had seen on the main YouTube website and app. The videos included images of clowns with blood on them, scary advertisements and messages telling them someone was at their door. Ms O'Donovan said she was "very, very sorry for any hurt or discomfort" caused by the videos.