Ummm, so if you lie to a person, and years later they call you on it and you then admit it was in fact a lie, then it's not actually a lie in the first place? Interesting logic you have there.
I don't consider it a lie because as I told my daughter that it embodies the spirit of giving and as such "We are all Santa."
So using your logic, will you/have you never played peek-a-boo with your kids? Because the reason infants find that fun is they haven't yet learned that just because they can't see you doesn't mean you aren't there.
To their minds you are actually vanishing and playing the game would be "lying" to them.
That's basically your argument. So is peek-a-boo just as bad?