What is the plural of Elf of the Shelf?

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So, what's the plural of Elf on the Shelf?  Elves on the shelves?  But what if they are sitting on the same shelf?   Then would it be elves on the shelf?  Anyways, we read the story Elf on a Shelf to the boys tonight to introduce them to their their little Christmas friends  :)  We read it slowly and carefully, stopping often to check for understanding and to help clarify.  We want to make sure the boys fully understand what is about to happen!  They seemed quite excited, as Matthew was ready to start looking for his elf immediately after the story.  Tomorrow will be Bash and Dash's big debut...  its sure to be exciting.  Can you guess where the boys might find them?!?!