Most people who are that poor are not educated enough about reproduction to prevent childbirth due to lack of sexual contraceptives or information about safe-sex. They are born to absolute poverty and know little outside of their little town or country. Sex to them might just be seen as something you do with little to no consequence or something that just comes easily.

What you see as suffering might be seen as normal daily life to them which is terrible. The way most children in richer countries live might seem foreign to them. That being said, infant mortality is also very high in those countries so a chunk of those children born will not make it past 20 years old.

I do believe that as countries get richer the people of the country start having more responsibilities and jobs and those overwhelm the time available to take care of kids.