There's an interesting article in New York magazine on lying. While parents cite honesty as the trait they want most in their kids, there's a few set-ups that encourage telling tales and denying facts. The author notes that children observe our socially polite "white lies" and essentially get the lesson, "It's okay to lie to avoid hurting others," which they then extend to stuff like telling us falsehoods about their activities to spare our feelings. There's also an interesting discussion of how teens perceive open conflict with parents as bringing them closer to the 'rents, while parents view it as destructive. You can see how this difference in perspective might encourage kids to at least withhold information. Even tattling gets the spotlight: We essentially punish kids for being honest about someone else's behavior, and send the message that we don't care about their problems.
But are all lies created equal, and are all liars just doing what they learned by watching you? You could take certain parenting lessons from the article (which I recommend you read, it's too much to summarize here) like the value of having less rules, but both enforcing them and explaining why they are in existence; avoiding setting children up to lie (asking "Did you do that?" when you know full well they did); and recognizing that protestations of rules are an opportunity for discussion, not defiance of authority. I would add that it might help to soften the value judgement on lying, and recognize that dishonesty both requires creativity and intelligence (as mentioned in the article) and that catching your kids in a lie might be a sign they are protecting your feelings too much. And showing kids that making mistakes is normal and expected is probably valuable in the pursuit of truth as well.
But I think truth is often not as simple as "Did you kick your sister?" There's honesty in recognizing your own motives and feelings, almost independent of other people, though it influences those interactions. For example, what we call stoicism could be seen as a kind of lying at times. And frankly, I also wonder how much dishonesty can be solely attributed to modeled behavior and trial and error. My kid is almost frighteningly honest and direct, even when it would be in her best interests to lie (though I'd be curious to see if this behavior was consistent with other people as well.) I wouldn't say she got that from watching me, it seems more much innate to her. And that honesty can have social repurcussions as well, since she has to work harder to be gracious. Honestly? I guess I think it's pretty complicated.
