Definition of lying from my 4 yr old: It's when you say something that didn't really happen. Or you're not telling the truth cuz you didn't want to get in trouble so you want to tell something else that isn't true and that's lying. And when you know the answer, but you don't want to tell, cuz it's bad. So you tell the wrong thing, even though you know it's not that answer.
Definition of lying from my 3 yr old: When you be bad. You don't know the truth. And when we don't be nice to the babies.
This was an exact quote from February of this year copied and pasted from a message board I frequent. Just thought I'd share!