This will kill the rainforrest in Africa. Because the survivors will use it for bushmeat, wood, jobs, fields for cows, ...
You don't create a self-sustainable economy by destroying human capital.
tell this to those whose children die of hunger because of climate change.
Thus: two million children saved, is two million pregnancies less. (To a first order approximation. As people get richer, all kinds of things change over time.) You are right in some sense: people are replaceable, and they will be replaced. But at a cost in resources and of course emotions.
Even if you only cared about the rainforest, and not about people at all, the smaller ecological footprint should warm your heart.
https://www.theguardian.com/global-development-professionals...
"women want an average of nine, while men say they want 11."
Your pregnancy point is wrong though, so you say you save resources due to not having them start another pregnancy? Well the kid uses resources too and it does that at a increasing rate throughout the years. Once that kid has its own kids....you get the idea.
Unfortunately there never will be a global population control so all is left is this: upon a certain number we'll have a massive humanitarian catastrophe, most likely ending in the death of hundreds of millions due to starvation or wars. Not only will the environment suffer heavily, but once again humanity takes a step backwards towards becoming brutes again.
If less kids die in infancy, they will have less babies to make up the (negative) difference.
By the way, please have a look at http://economics.ucdavis.edu/events/papers/WuLeminJMPMalthus... and tell me what you think.