why do parent lie about santa not egsting?

Good question. 

Revelation 21

But to the cowardly and unbelieving and abominable and murderers and sexually immoral and sorcerers and idolaters and all liars, their place will be in the lake that burns with fire and sulfur. This is the second death.”

To create the magic of Christmas within their children, that adults can only relive through the eyes of their own children.  Trust me, your anger about being lied to will turn into regret that you ever found out and you too will miss the magic eventually.

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