From "Learning to Lie", by Po Bronson, New York magazine, 2008-02-10:
The most disturbing reason children lie is that parents teach them to. According to Talwar, they learn it from us. "We dont explicitly tell them to lie, but they see us do it. They see us tell the telemarketer, 'I'm just a guest here.' They see us boast and lie to smooth social relationships."
Consider how we expect a child to act when he opens a gift he doesnt like. [...]
Meanwhile, the child's parent usually cheers when the child comes up with the white lie. "Often, the parents are proud that their kids are 'polite' -- they don't see it as lying," Talwar remarks. She's regularly amazed at parents' seeming inability to recognize that white lies are still lies.
[...]
Encouraged to tell so many white lies and hearing so many others, children gradually get comfortable with being disingenuous. Insincerity becomes, literally, a daily occurrence. They learn that honesty only creates conflict, and dishonesty is an easy way to avoid conflict. And while they don't confuse white-lie situations with lying to cover their misdeeds, they bring this emotional groundwork from one circumstance to the other. It becomes easier, psychologically, to lie to a parent. So if the parent says, "Where did you get these Pokémon cards?! I told you, youre not allowed to waste your allowance on Pokémon cards!" this may feel to the child very much like a white-lie scenario -- he can make his father feel better by telling him the cards were extras from a friend.
(quoted passage appears on the third of five pages in the web version of the article)