Gwen: I know there is no Santa. Everyone knows that all the presents come from parents!
Me: Who is everyone?
Gwen: Everyone at school.
Me: Ok, if you are so sure, than do not write a letter to Santa and you can continue to loudly proclaim that "he doesn't exist" -- it really wouldn't matter if he truly doesn't exist. On the other hand if he does exists, he might get upset and skip our house entirely.
....
Gwen: Well, I'll write him a letter, just do not tell anyone.