How can Santa exist when adults buy the toys?
Why was this seen as off-topic?
Is world-building reserved for subject matter suitable to an adult audience?
If the OP (who is not me) is a children's author, looking for a plausible explanation for the weird behavior of parents in their Santa-is-real Children's story... How is that not world-building?
I do not know the OP, nor do I know that the OP is a children's author. I'm involved here only in self-interest: I wrote a really cool answer and the question got closed moments before I could post it. At first, I posted my answer as three-successive comments, then I thought better and deleted those comments so that I could bring the discussion here