Parents "lie" to their kids about things like Santa because they remember the magical world that was created for them from their own childhoods, before the reality of a world with no Santa, murder, disease, death etc intruded on their reality.

Which is better, telling your child:

"yeah you will lose all your baby teeth and each one will hurt and bleed and make you look silly with big gaps in your mouth"

or

"oooh you lost a tooth, now let's put it under your pillow and the tooth fairy will exchange it for a little gift while you sleep"