what is the story behind elf on the shelf

The tradition of Elf on the Shelf began with a special elf who was sent from the North Pole to help Santa Claus keep an eye on children's behavior. The elf's name is Buddy, and he is assigned to a family for the Christmas season. Buddy's job is to observe the family's behavior and report back to Santa about who's been naughty or nice. Every night, Buddy returns to the North Pole to report back to Santa and then comes back the next morning to his assigned family. Buddy is a fun and playful elf who can get into all sorts of antics while he's away from the North Pole.