Odd as it may seem, children who hit are children who are afraid. The fears that cause trouble for a child who hits usually have their roots in some frightening experience earlier in her life, even though she may not seem frightened at all. To manage her fear, the frightened child develops aggressive behavior that flares any time she feels tense. Instead of crying or saying she feels scared when her fears are triggered, she tightens up, can't ask for help, and lashes out.   

You don't need to know why a child is fearful, in order to help her. What's needed are measures to increase her sense of safety and connection with you, whether you are her parent, her caregiver, or a loving relative or friend.