Kids are mean. My mom used to say that to me when I was young, and I never fully understood what she meant. However, as a mom of 4, with one of them being 9 and going through some physical changes...I totally see what she was saying.
I'm glad for you that your son didn't pick up on this. I do think it can be more hurtful as a parent hearing and seeing this (if they are too young to pick up on the verbal stuff). I too, have worried and stayed up late thinking about how to deal with this. Do I go to the parents? Do I ignore it? Its a tough answer. If I was the parent of a child who was picking on another kid, I personally would want to know so that I could deal with my child on this obvious character flaw.
I too have listened to other kids pick on my daughter (her teeth aren't coming in straight as well) because of her teeth, her hair...whatever. I spent almost an entire year dealing with tears over what other kids were saying. Here's how I approached it: For starters, her confidence can't be in what other people think about her (or him). Words are just...words. I tell my daughter to repeat to herself...sticks and stones. When she was older I explained to her that some people are just not confident in themselves or their abilities, so they find other people to pick on, to get the spotlight off of themselves.
I encouraged her to not retaliate. After all, that would make her a bully herself. I encouraged her to be kind, but definitely not go out of her way to try to please these kids. I also encouraged her to do her best to ignore what other people said (if it was continual, then she would have to take it to an adult for help). I tried to remind her of how she was loved by MANY and had many friends who loved her for who she was.
I took the time to teach her that her value as a person was not determined by what others said. It took a full year (for us) before I think it sunk in and she stopped worrying about what the girls were saying. Now, if it happens again, she tells me how she ignores their words and will go look to find her other friends.
I think this becomes a real teaching and growth opportunity. Its certainly not fun while your child is going through it. Try to take a positive spin on it with him (as he gets older) and use it to develop his character- because it most likely will. Teach him the value of being a true friend. Teach him about how words can be used to uplift or destroy ...there are limitless opportunities to teach in these situations. I believe that we are accountable before God with our speech. I try to teach this to my kids as well.
Sorry so long. Hope this encouraged you.