...by telling my 6 year old not to hit / kick back in school? 
Our 6 year old is such a lovely, sensible, wise young man and so caring and gentle (polar opposite of his younger brother!) There have been quite a lot of incidents in his school where these twins like to bully everybody (mainly the girls) but long story short, we have had numerous meetings with school about this as our son was on the receiving end far too many times.
My concern is that, at this age, I haven't really brought him up to retaliate (don't get me wrong, I don't see anything particularly wrong with teaching your kids to do so) but my boy is so gentle and always reacts very maturely when it comes to these things 
People (especially my mum) keep telling me he needs to 'toughen up' and I ought to be teaching him to hit back / kick back - am I and have I been doing wrong by telling him not to, and instead to just take himself away from the situation and tell a teacher? 
worried mum x