Living in Italy, I can see what life is like after years of a falling fertility rate. Italy has the lowest in the EU, and you can literally see it.
It has plenty of social implications. The way a family cares for the one child, sometimes two. Money. Politics. Even parenting itself is effected. You would never want to upset your one child. After all, when you get too old to look after yourself, who’s going to take care of you?