For example, what kind of story would Geralt the Witcher tell his kids? “Once upon a time there was some normal everyday shit that went how it always goes”?
Must be the equivalent of realworld kids saying “Daddy tell me the story about the Tesco delivery again! The one where they forgot the 2L bottle of Pepsi Max!”
Many fantasy worlds start on the premise of “how was the world created, how many gods do people worship?”
By simply modulating that you can get a lot of fresh ideas.
Maybe in a fantasy world it would be more conducive to have the stories grounded in reality. Kids need to know how to deal with trolls and goblins.