Then I realized, what a step forward their brains took!
Lying is a development in our brain that isn't inherently evil, but instead much more like a brain first learning that it can experiment with different messages.
Love them, and let them see you seeing through the lie. Better to say, "nice try kiddo, I understand that you feel bad about blah blah blah" then fear that this is the beginning of a life of crime.
Besides, if you never notice them lie to you, you might have a sociopath on your hands!