Why not one kid and try to use the excess parenting bandwidth to equip him/her to face the new world and maybe even fix it a bit?
That is, one kid per woman halves the population. If the axiom is at least maintaining, ideally growing the population, every woman needs to give birth to at least two and ideally three or more kids.
Of course, this isn't to say I'm telling other people what to do regarding offspring, because I hate that kind of intrusive attitude. I've already decided I'm having no kids, because fuck the human world; and anyone who comes bitching at me about it one way or another can take a hike and pound sand. So I'm not going to be hypocritical and turn around and tell other people what to do in the bedroom.
But if the purpose for all the noise behind childbearing is to take population count trends out of the negatives, advising "one kid" not only doesn't help solve the problem but actively makes it worse.
As for what decafninja (or any individual for that matter) decides upon in the bedroom, that's for him to decide and his business alone. I'm not going to comment because it's none of my business.
I'm just pointing out that in a wider discussion of "oh noes population decline oh noes low birth rates", it's not constructive to be talking about having 1 kid when there's a hard minimum of having 2 kids and ideally more.
If people voluntarily self limit the size of the population that is a good thing because it means we won't need to shoot each other if it turns out we are straining the earth too much.