You're completely and utterly ignoring the fact that raising children, especially multiple ones, is an extremely difficult task, even for two people. I know of very few people who would opt to do it themselves, even if the financial incentives to do so were worth it (they aren't even close).
I just want to point out there are a lot of poor women raising significant numbers of children. The woman next to my mom has 5-7 (it's hard to tell, and she just had a new one). They father (of some of them) is around a little, but mostly not around. And it looks like there are several fathers. Yes, raising children well is hard, but I would not describe what this woman does as difficult. Older kids are raising the younger ones, etc, etc.
So, I would definitely disagree with your assertion.
I don't have as good of an answer for reducing children. It would probably be best to work on reducing the number of children by providing easier access to birth control.