My hypothesis is this: If a kid (aged about 12 or older) knows how to be a good liar, and how to spot other (good) liars will actually be more honest, or at least be able to be in relationships of higher quality in the long run.
I'm setting the age limit at 12 because a younger kid who can lie without you realizing it would be a nightmare.
Please note that I don't have kids. In fact I'm not even in a relationship but I'd like to hear your opinions. I was looking for a psychology site but didn't find one on SE. If you think my question is a better fit for another site please flag it.