Most first world countries don't need nor even want to encourage people to not have kids. In fact, most want the opposite. Countries like Japan and Sweden are actively pursuing measures to encourage people to have more children, because their countries are looking at existential crises as the result of having too few young people, and a population that isn't replenishing itself.

In fact, the US, which offers tax breaks for families with more children, is right around what is considered the ideal birth rate as it currently stands. Projections for increased global population are being driven almost entirely by developing nations, most of which are in Africa. And most of the reasons for the high birth rates are entwined in a very complex web of factors, including poverty, education, and general health outcomes, none of which can be solved by waving a magic wand. The good news is that these countries are projected to level out their population growth as they do develop. The reality is that it will take time.

But this means that anyone who seriously considers "population control" as the means to dealing with climate change, world hunger, etc. completely misunderstand the realities surrounding both the growth of the global population and our ability to influence it. And that is without even considering the history of what "population control" has often meant, and the fact that it is a slippery slope that has been used to justify war, eugenics (if not in name then in function), and genocide, to say nothing of a whole host of societal issues like sexism.

Population control is not "the solution". "The solution" will require finding ways to make our societies sustainable at the increased population levels.