My son was 2 1/2 when he was being hit and picked on every day at my gym daycare by a 3 year old. My kids were all FIRMLY disciplined for hitting before age two, so my son KNEW hitting was wrong and he didn't hit back (and they say spanking teaches kids to hit). He was crying when I dropped him off, and finally I found out from the daycare lady that a certain bratty kid, who was aggressive with everyone, had been targeting my son. She was putting him in time outs (just like his mommy) so of course every time he popped out of time out, he would slug my son. I didn't blame the daycare provider for not being able to effectively discipline the kid-not her job, but I did blame the mom. I confronted the mom and asked her is she was disciplining her kid for hitting, because he was always hitting mine. She gave some load about logical consequences and time outs (I know what the logical consequences are for slugging people actually, and it's not that the victim will put you in a time out).
That DAY at home I taught my son that if a bully hits you, First you yell "STOP IT!". If they hit you again, you hit them back. I then rehearsed with him and let him hit me and knock me down by pretending to be the bully. The next day at the day care, my son was getting nervous at drop off, so I reminded him and encouraged him what to do about the bully. I told the daycare worker my son had permission to defend himself and she was all for it. I heard the screams from the treadmill. The bully hit my son, and my son hit him so hard he fell down. The mom was in hysterics (the kid was also a tantrummer, so he had everyone convinced that falling on the carpet had caused him insufferable damage and was screaming at the top of his lungs). I gave her that "really?" kind of look. The kid never hit my son again. He did however, hit an infant in the head with a heavy toy truck -which the infant's dad did NOT take kindly to-at which point they finally quit coming to the gym.
Now my son is 3, he speaks up and yells at aggressive kids at the park. He knows how to identify the mean behavior and not to side with bullies EVER. He hasn't had to fight back again, but he knows he can and should, and when he's 4, he's going into Tai Kwon Do (the starting age here). I had the same lessons and rehearsals with his big sister, now 5, and they both defend their youngest sister (2) who has a large birthmark on her face which draws a lot of mean comments from other kids. She'll be getting the self defense lessons big time soon.
If my kids ever get into fights at school, I'll know if they were retaliating or not, and I'll have their back one hundred percent. And if they get in trouble for fighting at school, even for retaliation, I'll back up the school in their measures, and home school during their suspensions, but they won't be in trouble with me, because the important thing is that other kids know they are not targets. So that whole, "You're kids can't hit back because of school policy" is not my concern. My kids know right and wrong, and they can hit back.
Explain to your son, if someone snatches his toy, he can yell at them and snatch it back, or let it go if he doesn't mind. Rehearse. If a kid speaks meanly to him, he should speak up right away, "Hey, that's mean." Rehearse. If a kid hits him, he should yell "Stop" and tell someone, or hit back. Rehearse. He needs to get comfortable with this, because if there is a delay in self defense, the bully gains power. Speaking up right away will put the bully off onto easier targets. These are not things a nice kid from a good home will know on his own. (mine didn't). Teach him how to react, step by step, clearly. It's actually good for the bully too, to learn at an early age what happens when you mistreat other kids, in case their parents aren't being clear enough.
Kids are really undisciplined and mean these days and their parents make excuses for them. I have heard really evil things being said to my youngest about her "ugly face" by 4 and 5 year olds while parents sheepishly laugh and ignore it with a "kids don't know better" shrug and NO action. My kids would NEVER get away with that kind of cruelty. You have to arm your son.
And there are lots of parents out there like SLM much more worried about the retaliators than the kids who struck first. Why isn't your butt on the line when a large child strikes a smaller one for no reason? Are you just as firm with the parents of hitters as those of retaliators? The whole point is that some parents teach their kids to ONLY hit back while others never even bother teaching their kids not to hit. My kids know I do not allow them to hit others (first) AND that other kids would hit them back if they attacked them. Both valuable lessons.
You can teach them to walk away and tell someone now, but it will be harder to teach them to stand up for themselves later than if you teach it from the start. All the most recent bullying studies have concluded that the turn the other cheek and walk away mentality was great back when society was stricter and your teacher or parents would actually handle bullies, but now kids must defend themselves, and walking away and ignoring will show the bully you're scared and they will continue to harass you. Most of the bullied, depressed, suicidal kids today never fought back.This is for slightly older kids, sure, but learning younger only helps. My son was like a new happy kid with the weight of the world off his shoulders once he knew what to do about a bully, He hasn't had to do anything since, and he's not aggressive. He's just not scared and crying before daycare now.
You know who doesn't like the "It's OK to hit back" philosophy? Parents of hitters who don't want to discipline it and want everyone else to tolerate it.