Talking to strangers

Why does it seem so difficult to make new friends? I had this discussion last night with my husband. He laughed at me when I told him I was disappointed that the other preschool parents hadn't tried talking to me yet. I was very excited for my son to start school, I figured I would make new friends, friends who had a child similar to mine, friends who would understand me and open my world to new things. He laughed and asked me if I was being serious. Of course I was. He seems to think I can be intimidating or even standoffish. I am sure I am at times, but I don't consciously do it. He then asked me if maybe I should try to engage them first. That thought terrifies me. I don't know why, I am usually a pretty open person. I admit I can be shy though. Friends have told me my shyness can come across as bitchiness. Pshaw. Then I expressed my feelings of maybe being excluded because we only have one child. From what I observed of the other parents most had multiple children. I often get the question "do you have any more?" When I reply that I only have the one I notice that I get a look. I could be imagining it, but I don't think I am. It was a miracle I had my son and maybe I still harbor some of the old feelings of not fitting in with friends because they had kids and I didn't.
Back to me doing the initial greeting, why am I so scared to do this? I am sure if one of the other moms said even a simple "Hi" I would be overly excited and probably bombard them with my verbal diarrhea. Sheesh, with both of my professions I talk to strangers all day, but this has me all a mess.