Questions on Hitting

1. How do you deal with a 3 and 1/2 year old boy who hits his 2 year old sister.
2. Sometimes these episodes include him hitting, biting, pinching, or scratching himself (with his fingernails) or banging his head on the wall. He has said, "I'm going to hit myself."
3. He will often hit or push his brother, myself, dad, or other children.
4. I have a happy easy going five year old boy who recently started hitting and scratching his 2 ½ yr- old sister and behaving much more defiant.
5. He hit me, so I had to hit him back to tell him that hurts me, he continued hitting me. What should I do??
6. 2-1/2 year old hits immediately upon not getting her way.