One or two children fair enough. More than that do you not start thinking there's less food to give my child, less time, less everything as I have to split my finite resources?
You're extremely ignorant, you seem to be inable to use complex thought to understand someone elses conditions. They simply don't know how many children are going to survive also their children are their safety net in old age as they won't have any social security.
When you're living hand to mouth its hard to give a fuck about concepts like pollution and excessive growth.
https://en.wikipedia.org/wiki/Demographic_transition