Whereas historically having kids used to be a "social" decision in various respects, it has now become a socio-economic decision for the reasons you point out.
If anything, I would argue that the economic shock of the pandemic (aside from the horror stories you hear from WFH parents who have kids) and the inequality it has exposed in our financial systems has cemented the idea for a lot of middle class millenials to have no kids/fewer kids.
....Which then means your extended family (and own children) are indeed a ‘retirement plan’, because the expectation is that they’ll be around to support you when you’re unable to support yourself.
But the intensely individualistic American lifestyle doesn’t lend itself to that thinking very well, so there’s less incentive for folks to have kids for their own interest.
(Indeed, as a mid-20s couple, we’re more often told the ways in which children _limit_ the lives of the parents, rather than augment them.)