Children only hear the last three words of what we say.  As a childhood educator,  I learned this in a training I attended and have found it to be true with my own four children.  So when we say "Please don't run in the house"  children hear, "run in the house" and get confused when they get in trouble for running in the house.  So when talking to your children pay attention to the last three words of what you say,  and this will help you in communicating with your child.