At this age, your child has no concept of right and wrong. If you were spanked as a child, you may think it is a good way to guide your child. Or maybe you don't want to spank, but you find yourself doing it because you don't know how else to get through to your child.
What you need to know:
At this point, you are physically bigger and stronger than your child. You know more than your child and, because your brains are fully developed, you are capable of greater self-control. When you try to get your child to behave better by hitting your child, you are indirectly telling your child that hitting people who are smaller and weaker than you is an acceptable way of getting what you want. Kids who are spanked who have a harder time regulating their emotions, and who get into more trouble. Kids who are spanked are less emotionally healthy than kids who aren't and behave worse over time.