I agree about not being able to understand lying. I think that not telling the truth could be a game they play, or like my daughter, sometimes she like to do the opposite. "Go get your shirt" and she brings back pants while giggling, or I'll ask her to sit down and she'll jump up. I just correct her and say something like, "that's not your shirt silly girl! Go get the shirt." and she'll get it. Or "mommy asked you to sit down, not jump up. I need you to sit now (with a stern voice) and she'll do it. I would just correct him when he is "inaccurate".
at 11:47 AM on Dec. 4, 2010