Answer:
I have read that the average number of children for a white woman in the US to have is 1.7, while the average black woman has 2.3.
So, not much of a difference; black women are more likely to have two or three children, white women more likely to have one or two.
Not much of a difference; probably cultural.
Of course there are many women of both races who have none, and many women of both races who have five, six, or more.
That sort of thing is bound to skew the statistics.