My mom pulled the wool over my eyes in epic fashion when I was nine---it was her crowning moment of awesome as a mom.
We went out for a Christmas party in the neighborhood on the 24th. My father had just passed away two months before, and I had outgrown the whole Santa Claus thing. My mom---well, she just wasn't ready to deal with that from her kids, not when their father had just died. She needed to believe that her kids were still kids, so it was as much for her as for my seven-year-old brother and me.
Anyway, long story short, she had my uncle Kevin (I didn't find out about this until I was 21 when my mom finally told me---and my then-girlfriend---the story!) come into the house, eat all the cookies, put the presents under the tree, and steal away into the night after leaving a note that said "Your dad still loves you. And you've been very good. - Santa" with the presents.
I called my friend Steve next door (never mind that it was midnight!) and said "Steve! Steve! He's REAL! Santa's REAL! He came to my house and everything!" (give me a break, I was nine!)
Best Christmas EVER.