A question I do have about Europe though... why are the birth rates so low in many countries? They aren't low here.
Whenever I visit the US I'm always struck by the large number of young people (under 30) with children....it's strange to me as we tend to have our first child in our early 30s and a family with more than two children is unusual.
Those who do have more than two children tend to be religious.
IIRC the birthrate in nearly all Western countries is below or barely at replacement levels...that's certainly not the case in the States so perhaps the question should be "Why are the rates so high in the US?"