The line comes from Doctor Who, where a mysterious child wearing a Second World War gas mask repeatedly asks for his mother while wandering wartime London in the 2005 episodes The Empty Child and The Doctor Dances. The repeated question became one of the show's most quoted creepy moments, and it later spread through reaction videos, horror edits and soundboards as shorthand for something innocent turning sinister. It endures because the phrase is instantly recognisable even to viewers who have not seen the full story.