I am not, because there has never, in my memory, been a single second of my life in which I wanted children. Not that I'm against kids or anything... after all, I was one once.
But I don't want any of my own.
I was once babysitting a little kid of about 4 or so, and he suddenly stopped playing and asked me,
"Do you have kids?" I said no. He looked up at me very seriously, paused, and said "...you should."
I assume it was his way of saying that I was good with kids. I guess he would know better than anyone, lol. I still don't want kids though.