Don't mess with my baby!

Why are kids so mean now adays???? My baby is starting to be teased about his weight and I hate it... I feel helpless and my baby is in pain! My baby is a little on the chunky side but I think he will grow out of it he eats good just not as active as most kids...It started Saturday actually during his party at the park some boys came over to him and started calling him some mean names, my son wouldn't eat nothing at his party not even cake (and if you know Devon that's crazy). I have always taught my son that you don't lash back at all... but now that we are actually dealing with bullying I want to tell him to knock them out (but I know that's not right). But then yesterday at school a boy in his class decided to call him names and push him around (what is wrong with kids????) Devon didn't lash back but he was really upset... I want to teach my son good values and to deal with situations the right way... I have told my son that first step is to ask the other child to please respect him and keep there hands to themselves and not to speak to them that way.... then to remove himself from being around that person if that is possible (like yesterday that wasn't possible for him they were in the lunch line) And then if the child doesn't stop go to a teacher or whoever is in charge.... is it wrong to tell my son that if he has done all of these things repeatedly and the child continues to harrass him that he can hit them back???? That is an awful question I know... I just really do believe that you can't let someone walk all over you over and over.... and I hate violence I really do just can't stand someone hurting my little man he is only 7 he shouldn't have to worry about little kids being mean like that... But he is a sweetie both days he got picked on those nights he prayed for the kids that had picked on him ( I overheard him telling God to help them, and that he knows he can't judge them cause he doesn't know what kind of life they have at home, that there mommy and daddy might not be like his) Things like this make me proud... I am apparently doing something right!