An average middle-income family with two kids spends more than $200,000 to raise each child to age 17, followed by college costs (and/or any other support). In coastal cities, the number is more like $250k. That price is rising faster than inflation at about 3%, and college costs are rising 4%+. To begin with, let's just ignore college and just annualize it all to $15,000/year.
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.