Less charitably, this is the kind of advice that mostly seems like an excuse to preach at people.
No, I just picked it as a random example of something that you can do to reduce population growth. Widespread access to birth control in developing countries would be a better solution. Supposedly educating girls in developing countries also helps reduce population growth as well. And there are probably countless other things you can do.
They also have traditions in many developing countries to have very large families.