My child is 3 years and 6 months and every child he seems to play with seems to pick up on his sensitivity and tease him extra. This could something really minor like touching him on the shoulder - which doesn't hurt him, it just annoys him and makes him cry like a baby. I don't know what the best solution is. I'm afraid that as he gets older it'll happen more and turn into bullying because my son is perceived as weak. I know that the children that tease him shouldn't be doing it, but I just want my son to toughen up and ignore it....It's really getting me down and feel like it's always my child that's crying a lot.
That's pretty common behavior at age three and a half. I would hesitate to call it "overly" sensitive at this point.
At any rate, it's not disliking being touched on the shoulder that's the problem, it's the reaction, so teach the reaction you want him to have and make him repeat it. It also helps to ask if their natural reaction is having the desired effect.
For our kids, we say, "Does screaming make him leave you alone, or does it make him bother you more?" "Okay, then instead say, 'Leave me alone!' and come and get us if he doesn't. Say it."
The important thing is not just to tell him to stop crying. You need to teach him what to do instead.
Our son who does the teasing has a hard time recognizing when the screaming is for fun or not, so we tell him, "Does it sound like your sister is having fun?" Our end goal is for them both to have the tools to prevent and defuse the situation without our intervention.
Without knowing anything else about your son - have a look in to "Sensory Integration". Some kids can be overloaded with sensory input, and have a hard time dealing with it. At the very least it could provide you with some insight in to his world.
If it seems to fit together you might want to get help on it - here in Canada we have the Child Development Assoc. who give free OT etc for preschool children with Sensory Integration Disorder (it's a disorder when it's a problem, and it sounds like it might be for him).
Generally I try with my 4yo to work on the underlying issue rather than prescribing a behaviour that he should follow.