Catholic families are the biggest?
I thought this was the funniest part of the movie, because it was way off. Not so much that Catholics aren't baby factories, but because Mormons are mentioned as better practicers of birth control.
Obviously the film makers weren't acquainted with Mormons (even though they mention them), or the ones in Britain don't have as many kids as the ones in the States. Muslims are pretty much anti-birth-control as well. The protestant depiction was pretty accurate though. Most of the Christian population decline in the west is coming from Protestants. I live in hardcore Southern Baptist country, and few Baptist families have over 2 or 3 kids. I was always an oddball with 9 siblings growing up. The "minimum" # of children for families in my LDS (Mormon) ward seemed to be like 4 (no, nothing like that is actually enforced...). I did know of some huge Catholic families though.