Growing up in poverty tends to stunt children's development permanently.

I'm sure it is true in the US too, though I don't have a study to point to. This is why we need a strong welfare system that lifts children out of poverty, not one that does only the bare minimum such as Clinton gave the US.

Of course, we also need to make it easy for poor people to avoid having children they can't afford to raise, by providing reliable contraception and abortion gratis to all women.