I suspect many of these stories came about to help parents control their children. Santa for example (He knows when you've been bad or good so be good for goodness sake.). Of course there are many people who say God is Santa Claus for adults. LOL! The tooth fairy is designed to make the act of losing teeth less traumatic for the child. Nothing like some cold hard CA$H to ease your pain. Some kids can't wait to loose their teeth! The Easter Bunny and Cupid are just candy bearing mascots. Santa Claus is the major lie.
Mankind has always needed to believe there was something bigger, powerful, and smarter then us. The majority of parents that "lie" to their kids do it with the hope of enhancing their children's life with fantasy and wonderment. Unfortunately I learned the truth about Santa Claus when I was only 6. I felt like I had to pretend I still "believed" because if I didn't my gifts would be clothes instead of toys. ha ha ha
Honestly it does appear to be hypocritcal for a parent to tell a child they should not lie after they have lied to their kids (for years). Then they explain it's a "white lie". LOL!
What makes the Santa lie even worse is it appears (the rest of the world is in on it with your parents)., Everyone from the Santa Claus appearing at the local mall to the television specials, movies, teachers, aunts & uncles, to the mail man accepting letters written to the North Pole! It's amazing most of us turn out fine after discovering the elaborate hoax!