Say “Thank you” often.
When children do something you’ve asked them, thank them. When children apologize to a friend, thank them. When you see them doing something right, thank them. Thank them often, and be sincere.
I’m not fond of the idea of giving children a treat for doing the right thing. In our classroom, everyone helps pick up because that’s how we take care of our room. We apologize to friends because that’s how we treat our friends. We do nice things for others because it makes them, and us, feel good. Thanks, guys.