Um. Yes. Yes I have.
Which led to the "Oh crap, which lie did he find out about?" moment. So I pulled up my mom pants and said, very seriously, "Yes, son, I have. Dragons no longer live, they went extinct around the time dinosaurs did."
(although really, even I don't believe that. C'Mon. There are caves somewhere in the world where a dragon is just waiting to launch himself into the night sky. It's why the ice caps are melting--- he finally woke up)
Sigh. Big eye roll. (I didn't know 7 year old boys *did* that).
"Is there any other lie that you want to tell me about? Because, otherwise, I don't know if I can ever trust you again."
I asked him, repeatedly, what he thought I had lied about. I got the above answer several times. Finally, we got to the heart of the matter. Santa Clause. Easter Bunny. And his reaction was not what I expected. "You shouldn't be spending all that money on me. It's too much."
My father had the perfect response to the Easter Bunny ("Rabbits don't lay eggs.")
But then we started talking about how the stories came to be believed. About magic, and how sometimes the most magical thing we can do is be kind to one another as that's what the holiday's are about. There's a germ of truth in the stories, in traditions. It might not start anywhere near where it ends up, but there is that little sparkly bit that takes hold and carries us away.
The myths and stories that define our childhood are only a jumping off point for most writers. It's where we learned in the magic of story telling, the magic of believing with our whole being. I don't know about others, but as a kid I constructed in my head a whole Easter City under a little hill with chocolate rivers and jelly bean paths and a basket manufacturing plant. Santa had the North Pole, so the Easter Bunny had to have his warren. It was one of the first lessons in World Building that I had.
Be kind with the stories and myths you tell your children. And when they ask if you ever lied to them... make sure you know what they're asking about before you respond.