OK, so humor me here. Why would a parent start off their relationship with their child by knowingly lying to them, repeatedly and emphatically about something the parent knows not to be true? That sound like a great way to get your kids to mistrust you. I have never pretended that Santa is real with any of my 3 boys and they have not missed out on any of the magic of Christmas. They know the true story of St. Nicholas. He was a good guy that helped kids along time ago. We still watch all the good Santa movies: The Grinch, The Santa Claus, The Polar express, but they know its just a story. People say "Oh, it just in good fun". I disagree entirely. For one you are lying to your child, which I believe puts a seed of doubt in their minds about what else you may lie to them about and you are taking away from the true meaning of Christmas: Christ birth. Now we don't over emphasize the Christmas story, but we do talk about it and my boys can recite most of Luke 2 and do several times for family during Christmas get togethers. They absolutely love Christmas and mostly because of the presents. So other than not believing in a outright lie, they have the same Christmas experience all the other deceived kids do.
So put yourself in your child's shoes. "I wonder what else they are lying about?" Its worth considering.