That's precisely why I don't want them. I don't feel it's worth the time and effort.
Not sure what your point about poor people is...
Merrill Lynch claims that an average retirement 'costs' about $740,000. Demographic breakdowns are much harder here, since they depend on both luck (health, mostly) and post-retirement location, so let's just use it as is.
The average age of first motherhood is 26, and fatherhood is 31. However, to my surprise, that's a bimodal distribution; let's use age 30 for our coastal/urban parents. The average age of retirement is apparently 63, so childrearing costs arrive 16-33 years before retirement costs. A stock market index fund held over the long term can reasonably expect perhaps 8% returns after inflation. Investing that $15k annually for 17 years should produce a retirement nest-egg of a bit over $2,000,000.
I tried to be pretty generous with my math here; paying for college, going from zero to one kid, or adjusting for cost growth all worsen the picture quite a bit. (Having >2 kids or living off the coasts improves it somewhat.) But the really damning part is that kids may not take care of you at all (it's a pretty heavy expectation), and even if they do most people face needs and expenses family can't take care of. If you have health needs that require regular care from a nurse, much less costly surgery, your kids are only going to be able to help by putting up money. And quite a few health problems like severe dementia make living at home with family nearly impossible by requiring full-time monitoring.
Living with family is probably a much better experience than living in a nursing home, and of course it's inherently rewarding for a lot of people. The data is irreparably confounded, but I wouldn't be shocked if people with kids are healthier and even longer-lived than comparable people without them. But there's really no salvaging the idea that having a family substitutes for an expensive retirement.
Studies probably do show that people with kids are healthier and longer-lived than childfree people. And "sucking it up" and having a kid or two like someone above says can give you this. However, this still results in a declining population, remember, which is what the main article was talking about in the first place. Every couple having 1 kid isn't going to maintain the population, for obvious reasons, and not even 2 will do it (you have to have an average of 2.1-2.2).
Now add to this the fact that more and more people aren't even getting married in the first place (which is improving the divorce rate), and not having kids, not necessarily because they don't want them, but because they can't find a suitable partner. I see this all the time here in the DC area on the dating sites: women who are 35+, frequently 40+, sometimes even 45+, saying they're never married, have no kids, but want them. 45 is a little old for a woman to have kids, and most likely if she hasn't found a man to her liking by that age, she never will.
This is a good point.
Even on the callous ROI level I was looking at, 1-2 kids is a particularly weird span. The first kid is most expensive and life-altering, so someone viewing kids as a retirement plan would almost certainly want to have a bunch of them. They're 'cheaper', it hedges against a kid not not taking care of you (for any of numerous reasons from a bad relationship to health problems of their own), and it makes providing care much more doable as a shared responsibility.
Honestly, a whole lot of social norms we took for granted actually seem to rely on families having 3+ kids who grow up to live nearby. Some mix of "community support" and "network effects" mean that the difficulty of raising kids has gone up substantially as family size and proximity have gone down.
Why does childrearing look so hard and expensive these days? Well, you probably don't live near family members with their own kids; my grandparents freed up time by trading 'daycare' with their multiple siblings who all had families.
Why does taking care of parents seem so rare and demanding? (Partly because we've improved longevity ahead of good health, so there are more parents who genuinely need specialized care. But also...) It's relatively easy to have a parent move across town into the spare bedroom that freed up when your kids moved out, and have your siblings come over when you're out of town. It's way harder to uproot your parents to come live in your one-bedroom apartment, or leave your job and friends to move back home and care for them alone.