Given that she only has two kids, maybe she hasn't yet figured out how children are made?! ;-)
The cultural consensus that children are very frightening, so *of course* we all want to limit their numbers, is overwhelming. People don’t even realize they’re being rude, because they’re just expressing what “everyone” knows.
The Pope, I believe, has hit on a key point: “arrogating” the power and authority to control life. It’s more socially acceptable to have a large multiple birth through IVF or ovulation stimulation that it is to have a large number of children, over many years, through the natural processes of marriage. The former shows that you’ve taken control, and the latter is frightening because you haven’t planned and deliberately caused it.