Hi JL, I agree with all the other moms, but I wanted to throw in my two cents on one other thing. you need to sit down and talk with your son. he needs to have the tools to be able to tell the boy to "stop hitting me. I don't like it. It's not okay" And then if the situation continues to be able to go and get the teacher. My son was also very gentle hearted, and whenever we would go to the mall (lynnwood mall! yeah) there always seemed to be some kid that would pick on him, be it hitting, spitting, or just being mean. It broke his heart, and mine as well. I have always been an advocate of "walk away", but sometimes that just doesn't work. So, I know this is a little contoversial, but this is what I told my son.
If you get hit you....
1. Tell him "stop, don't hit me, I don't like it, don't do it again"
2. If he does it again, go and get an adult. Usually it was me, and I will go with you and talk to the boy to tell him, "stop, don't hit, he doesn't like it"
3. If he hits again, defend yourself.
by him having the knowledge of what to say to defend himself, we never got to #3. At 3 he is old enough to tell people to leave him alone, and then get his teacher if it doesn't stop. That skill will last him a while throughout school.
Good Luck