when does elf on the shelf appear

The Elf on the Shelf tradition started in the early 2000s. It's said that Santa Claus' elves are tasked with observing children's behavior and reporting back to Santa Claus, and they do this by visiting homes and moving around each night to monitor children's actions and make sure they're behaving. Parents are encouraged to hide the elf each night and have the elf move around the home, sometimes in the most unexpected places, as a way to remind children that they're always being watched.