This is a tough one I'm sure I'm going to face at some point. My son is 16 months old and is lagging behind on the height scale. As things look he won't be the shortest in his class but he will be below average at the current growth rate.

That said your son being 4 years old is at a difficult crossroads. He is at the point where he is experiencing fear, anger and frustration but does not understand how to deal with these complex emotions. He understands rules and the concept of rules and looks for approval from others. His response to this situation may be some confusion about your rules of being polite and his looking for your approval and thus the passivity.

The tricky part is dealing with his limited understanding so be careful how you proceed. Understand that being picked on can lead to future self esteem and confidence issues. Teaching him to solve his social issues with violence can have negative effects as well. I would start by talking to him alone and get a gage of how he perceives this behavior from the other boys. I would encourage him to talk with you or your wife if he is having difficulty or if he is feeling threatened. I would also encourage you to speak with the bully's parents about their sons behavior and inform them that you will not tolerate unacceptable or dangerous play.

One other difficult issue here is your feelings about this incident. You need to determine how you really feel and make sure you are not overreacting out of a feeling of pride or shame. Sometimes it is difficult to see your son being less dominate and that feeling causes you to react. This may be a learning experience for your son and given some time he may learn to work this out on his own. I would observe this interaction for a bit longer and look for patterns before I would react.

Lastly...Teach your son respect, not only for others but respect for himself. If he feels threatened or uncomfortable he has the right to say NO. Walking away is the best policy; however, this could also be construed by the bullies as a sign of weakness. That is where things get even more tricky. This is why it is best to talk with your son and get his feelings about the situation. If you build on his self esteem and confidence he will come out just fine.

Good luck,