The elf on the shelf is a super cute idea but be aware it does take work!  My 8 year old and 4 year old understand the story and are very excited every morning to see where the elf ends up.  My older daughter has asked those questions you would expect. The only thing I don't like is for the kids on the fence (believe or not believe) I think that this could give some more doubt.  Probably better for ages 3-6 years. I do wish I would have got it when they were younger.