Pick any you would like, do a simple google search. The reasons people have children really has a hell of a lot less to do with anything noble as it does a selfish need to live vicariously through something we feel we as human beings have stock in, meaning our genetics.
It's specifically why we have PSA's about adopting pets, but almost none about fostering kids who go everyday without a mother or father, and I am not talking about little infants either.