But most couples I know wait until their 30s to have children. People want to have their own life, they want to have a successful career. When you see life in these terms, children are an impediment. At most you'll have one, more are rare. There has long been an assumption that low birth rates were better than high birth rates.
Fewer people put less strain on the resources of the planet.
And anyway, as a country becomes richer its people always have fewer children. But Europe, unlike the United States, has been resistant to immigration. This is terra incognita. If these trends continue, in a generation or two there may be countries where most people's only blood relatives will be their parents. Yes, I think it would.