Romney had 5 kids and he's rich. Of course, the extreme is that Jim Duggar guy who had 20 (the last one died as a baby, unfortunately).
There are more than a good share of rich people with lots of kids (that being defined as a minimum of four).
not sure on the us stats for this actually, i would only guess poor people have more syblings than rich kids, all over the world. i may be wrong.
And I think the average american family is larger than a swedish.
In sweden its definitely so that the upper class have less kids - 1 or 2. while the middle and lower have more. the lowest class is immigrants on welfare and they have 4-6 kids it seems.
The swedish average is known as 1.5 kids per couple.