I can soooo sympathize! I was extremely mad (at infertility in my case) as my son was an only child for 5.75 years. And yes, I had those conversations with preschool teachers, and family members. But I REFUSED to believe that being an only child is a bad thing! I REFUSED to believe that not having siblings would some how scar my child forever. I REFUSED to believe that being an only child made my son make bad choices or act up. Your son is a good kid too and don't let others sterotype him!
I've met plenty of only children who weren't bossy; my son wasn't one of them but they exist. I am convinced my son's inborn temperment was to blame, not a lack of siblings. Its hard when you feel guilty like you caused this. You didn't. Its not your fault, okay?? I hate so much when people sterotype only child. Drives me insane. If that teacher even thinks those thoughts again; you call me! I'll take care of her. Because actually, research shows that only child pretty much display the same personality characteristics of first born kids. So, there you go! Feel better!