I was so nervous to try this out.  I didn't want to blow Christmas/Santa for my 6 year old.  I worried that he might not buy into it, and therefore might not buy into Santa anymore either (he might start questioning it all).  I think it's incredibly important how you introduce this, so make sure you put a lot of thought into it.  I decided to create a letter from Santa & snuck it into our mailbox (and had my 6 year old get the mail that day).  Santa told them (6 & 3 year old boy) that because there are so many children in the world for him to watch over, he's decided to send one of his elves to watch over our family.  I think it's incredibly important to immediately address WHY you're getting an elf right now (when you didn't before) and why YOUR house is getting one, when not everyone's house has one (I was worried about kids at school).  Santa's letter announced that the elf would be arriving that night, so to watch for him in the morning.  The next morning the elf showed up sitting up in the Christmas tree, with the book about him underneath the tree, and a handwritten letter (Mom's left-handed writing). It was a flawless entrance, and my 6 year old believes it all even MORE than my 3 year old!  He was instantly writing letters back to Santa, asking our elf to take it back to Santa that night, etc.  The rest of the month was SO fun, not only for the magic in my kids faces each morning, but for the fun my husband and I had each evening getting the elf set up in new fun ways.  Make sure you have a plan in place for if they touch him (there need to be consequences or they won't believe he's magical), and make sure to set a daily reminder on your cell phone (I did 10pm).  You don't want to blow it by not having moved him one day.  They almost cried the day he had to say goodbye!  On the last day he was holding baby Jesus from our nativity, leaving a note to remember that while Santa & presents are fun, remember that Jesus is the real meaning of Christmas (we're quite religious normally, so I had to tie it in somehow, without being the lame family that doesn't allow Santa stuff at all).  ;)  Definitely recommend!!!