I think the underlying causal factor of both is actually phones/social media.
Even now in the Korean-American community, the running joke is that if one suddenly starts going to church in their 20s, it's only because they're looking for a romantic partner.
If the bar was the primary Western common area ("Where everybody knows your name..."), then its disuse leaves nothing to replace it.
Life... uh... finds a way.
(people keep forgetting how much reducing population growth and teenage pregnancy has been an explicit policy goal for decades! Getting it down to replacement rate is good, now we're arguing about the other direction needlessly)
About children the case is quite obvious. We created the cultural environment in which children are considered no less human than productive members of society and deserve if not the same amount of resources, then more. This order aligns well both with Western worldview and with human biological nature, so people are easily accepting and strengthening it.
But if we are spending on a child as many resources as on productive members of society, that means for fertility rate 2 we should forgo half of our resources. So on average to forgo half of your work for children are not very tempting, but to spend on children less is sociocultural unacceptable. The only solution? Less children.
I think fertility rate 1.5 is already pretty high for such environment and only show how strong biological drive to procreate for humans is. And government's attempts to increase birth rates by spending more seems like rather terrible idea: that only will increase cultural expectation on children costs and effectively will lower the birth rate even more.