This is certainly a fun "proof."
http://survivingtheworld.net/Lesson821.html

We chose to let the elf out of the bag when our son skipped into 5th at age 8. His 4th grade class seemed to be evenly split, whereas the 5th graders were primarily non-believers. We didn't want him to fall prey to any teasing.

We set it up as a right of passage for him, and that he was now taking on the great responsibility of preserving the joy for his younger siblings. In case the warm-fuzzy approach to requesting his cooperation didn't, we threatened a stocking full of coal were he to blow it.

So far so good.

Being offended is a natural consequence of leaving the house. - Fran Lebowitz