Both of mine lie and it is over silly little things like who left the peanut butter out on the table. I don't understand why they lie about things that don't really matter and we have explained that if they lie about the little things then that makes us doubt them about the big things.
Like HowlerKarma, we punish lying and that punishment is worse than what the initial punishment would be if they had told the truth. We always give them the opportunity to tell the truth and remind them that the punishment for lying is worse, and that sometimes works, but not always.
Luckily, DD9 isn't very good at lying and I can tell with her. DD7 on the other hand doesn't miss a beat when she lies and she will play the sympathy card when we doubt her. She is bound for some type of career in drama - I swear!
