I don't know... I have kids, neices, nephews, great-neices, great-nephews, lots of friends kids and now friend's kid's children, lots of kids in the daycare that I worked at... I have no idea how many kids I've loved and worked closely with over the years, well into the 100's at least.
Not one of them ever suffered a crises of faith in Christ due to finding out that Santa was a fairy tale. Not a one.
I think the big difference between stories, fantasy and otherwise, and faith in Jesus is the Holy Spirit. If our kids believe in Jesus (which almost all the kids I've loved have) then they also have the Spirit helping them discern the realness of Christ. If the child doesn't believe in Jesus, then believe in Santa or not is the least of one's worries....
Every year the question of Santa comes up on this forum. Most years I've asked one or both of my kids if they ever suffered a hit in their faith in God because we played out the Santa story... Every year they laugh out loud at the very notion.
Make believe and fantasy has its place in our lives. If some don't want their kids to have make believe and fantasy in their lives...OK...as a parent one has the freedom to keep your kids firmly planted in mudane facts. But, for those of us who allow fairy tales, fantasies and make believe, Santa fits in pretty nicely and becomes a fun holiday tradition.
It's really no exaggeration that I've loved 100's of kids. My large family, even larger church family and my previous profession as a pre-school teacher in a church day care has placed many children in my life. If it is a fact that children are indeed harmed by the Santa story...fact that their faith in Christ will suffer because of it, then I should be able to think of a number of kids in which the sad "fact" played out. Broken, no longer believers because their parents "lied" to them about Santa. As it it, I cannot think of even one. As a matter of fact, a lot of the children I have known are now parents themselves, Christian, believing parents and they are happily playing out the Santa story with their kids as well.
Is Santa a lie? Only if all fiction and make-believe is a lie. If one truly believe this is "lying" to children, then one should not participate. But, there are many Christian parents that believe no such thing and find the very concept actually rather silly. (The silly part being that our Lord has so little actual realness that children who were allowed make-believe and fantasy in their lives will come to not believe in Him.)