The average carbon footprint of an individual is however much larger for rich countries. It is true that n_children is higher for say, Nigeria rather than Germany. However n_children times footprint_of_a_child is much higher in Germany.

Using the very limited numbers from this wikipedia page [0], the carbon footprint of a German individual is about 15 times more than a Nigerian individual. Yet Nigerians "only" have 3.7 more births per woman than the Germans, and that's without taking into account the enormous difference in life expectancy. Taking the two numbers, the carbon footprint of the average German couple fertility behavior is about 4 times bigger than for a Nigerian couple.

[0] https://en.wikipedia.org/wiki/List_of_countries_by_carbon_di...