how to explain elf on the shelf

Elf on the Shelf is a magical tradition that brings the spirit of Christmas to life in homes around the world. Each year, Santa sends a special elf to a family to watch over their children and report back to him with all their good and bad behavior. The elf, who is invisible to everyone but the children, has a special magic that allows it to move around and even talk to the children. The children must be good and keep the elf safe, or else they risk missing out on receiving presents from Santa.