I need to rephrase the last question?

my son is three he was at a party with his dad he wasnt around the kids his cousin hit him in the face i dont condone to my son not defending his self and i teach my son his numbers and abcs and how to read he think that fighting is bad i dont beat my child light most parent s from where i am from but i would like for my son to fight back what should i do and i only need serious answers please