My grandmother told me she would have given birth to a dozen children, if she could have. When I asked her why, she responded that twelve seemed like a nice number. In contrast, my mother deliberately chose to have two children, spaced eight years apart, so that she could raise them as “two only children.” My grandmother remarked ruefully, “I never understood your mother.”Nowadays, families of more than two children are as rare as ice cream in the sun. Typical family size...