Why do some children won't to be bully to other children in school

First I won,t to start off by saying I keep to Young children in my home, I have being keeping them for a very long time. When one was just 3 month old, and the other one was 2 month old one is a girl and the other one is a boy. The boy name is Chad and the girl name is Chase they ages now Chad is 5 years old and Chase is 3 years old. Chad is in pare,k this is his first year in school and he is having problem with one of the kid in his class his name is Cole,he is the bully in Chad class. Chad come home everyday saying that Cole hit him in his stomach I ask Chad do you tell your teacher and Chad, say yes I told my teacher but Cole, still hit me any way Chad mother have talk to Chad, teacher about Cole and the teacher have talk to Cole parents. But Cole still hit Chad everyday and Cole also hit the other children also. It might be wrong but I told Chad to hit Cole back I told Chad you got to defended yourself from other children like Cole because if you do not hit them back they will content to hit you. I remember when I was a little girl I was in the 6 grade and this girl stay back for 2 years in the same grade and she was a lot older then the rest of the children and she was a bully and she will pick on all of the children in the class room. And I will tell my mother and my mother will talk to the teacher and the teacher will talk to her about hit on the children and that will not do any good so my mother told me to hit her back and that what I did so she stop hited me so I hope that will help Chad.I also remember when my daughter was a little girl she was not in school she was at home in our neighborhood, it was bullet hit on her and they was a lot old and bigger then my daughter. And I told her the same thing, I won't to ask you all a question, how would you handed that problem if you have a child in school that where being bully by another child. I did some research on it athere are some of the things I find out. In some children behavior come from there home because children look at parents as a role model. I give you my answer on this question but I am going to ask you how do you tell your children to deal with bullying/getting picked on in school. This is another question what can you do if your child is a bullying others children. If you wont more information on this subject go to bullyfreeworld.com