Here is more info I took from wikipedia.org about Elf:
The story describes how Santa's "scout elves" hide in people's homes to watch over events. Once everyone goes to bed, the scout elf flies back to the North Pole to report to Santa the activities, good and bad that have taken place throughout the day. Before the family wakes up each morning, the scout elf flies back from the North Pole and hides. By hiding in a new spot each morning around the house, the scout elf and the family play an on-going game of hide and seek.