The important difference between the two examples is the intention and long-term results of each. For the first, even though you mean it as a way of increasing their happiness, eventually they will find out the truth, sometimes with devastating consequences.
For the second, the technical lie was only used to cover areas that the child wasn't ready or able to understand, and, as she grows older and understands more, she will also understand why you simplified such a complicated concept and won't resent you for it .
What, DeadlyDad, you got something against Santy Claus? Why is the girl so understanding about the baby in the belly and yet she is damaged forever when she is told that there ain't no Santy Claus?
The girl is unhinged. Watch out! She might burn down an orphanage if she hears the truth about the tooth fairy.
The semantics of the concept "lie" in all languages can be found in the deliberate distortion of reality by someone for their own personal gain, even if their personal gain is only a perverse desire to cause others pain.
White lies, etc. are not lies at all. They are merely
culture memes for the larger good.
