For myself, I never wanted kids. I know that many many people don't understand this. I still get asked (even though I'm past 40 now) when I am having kids... and then inevitably the asker tells me that it is "not too late" and their cousin-neice-friend-sister had a baby when she was 53 and I could still be a mother. I just don't want to. I think the world should be grateful for that.
Fortunately I am blessed with many children in other ways. I have the cutest niece you've ever seen. And I moonlight as an occupational therapist working with kids a few days a week. Kids have a way of pointing out the things adults tend to miss. And the joy they spread if given the chance is infectious.