what is the story of the elf on the shelf

The Elf on the Shelf is a mischievous and magical elf who watches over children and reports to Santa on their behavior. The story goes that each year, Santa sends an elf to every child's home to watch them and report back on whether they have been good or naughty. The elf's job is to make sure children are behaving and following the rules, and if they are, the elf will stay and play. But if they are not, the elf will report back to Santa and he may not get any presents.