Talking about how Duplo has just started hitting reminds me of another thing: Duplo is really good at apologizing. If he’s done something wrong, telling him to stop does nothing but make him more angry. Giving him a timeout works better, but the best way to get him to change his attitude is to ask him to say sorry to the person he has hurt. He’ll stop dead in his tracks, give the person a hug, and say “sorry.” Then it’s over. He feels all the way better.