The only Mormon that I know reasonably well has five kids, so they're at least doing their part.

The main thing I've noticed among my peer group is that the more "career-oriented" you are, the fewer kids you're going to have. For those people it seems to come down to a decision that the expenses of kids outweigh any benefits.

Whereas the less well off people I know tend to have larger families because you're never going to have enough extra money for it to matter anyway, so why not have more kids and enjoy them.

Looks like Mormon and Catholic fertility rates are declining also (just not as fast as the population at large).

https://religionnews.com/2019/06/15/the-incredible-shrinking...

https://www.catholicnewsagency.com/news/empty-cradle-empty-p...