The guy who doesn’t have kids paid it indirectly in his social contributions. The next guy next to him too. And the next guy. And so on.
It's incredibly hard to budget for children though, you can't really foresee how much they will cost. One child eats little, one eats much, one is picky, one not, one likes soccer, the other one likes lego. Very hard to predict, except maybe year 1-2. But then one might be good with breastfeeding while the other might require formula and the cost of the first one is 0 while the second one could be very high
And I'm not saying it should be more, I was more saying it in jest to help deter comments like "but you get tax kickbacks!". I do think that we should be doing more for children - free school lunches with no means testing, free childcare from birth instead of just when they enter the public school system, and so on - but the child tax credit is the most visible "kickback" so I made a joke about it to acknowledge it.
My point here, more generally, is that companies shouldn't be trying to play this game with "fairness". Just call it what it is - capitalism and the invisible hand of the free markets. If people have problems with how that system allocates capital, then do something about it, but don't try to pretend any of its machinations have any relation to notions of justice or fairness.
(And I say this as someone not overly invested in that world - I have a 17 yo stepdaughter, and I am fortunate that in addition to my excellent healthcare, my company pays 100% of the premiums for my partner and kid, not just me).
My point is, people are going to have different lifestyles that cost different amounts and give them different benefits. Companies should fuck off pretending they care about fairness or cost of living. Just call it what it is - competition-based pay. You pay someone in SF more because you are forced to by market conditions, and if you could, you would pay them less, with zero concern for their rent or mortgage. And since you CAN pay someone in Kansas City much less, they do.
We've already seen the prevalence of remote work change the equation. Many places now pay SF 110% and everyone else in the US 100%. The COL difference between SF and KC is not that 10 percentage points. Nor could you compensate someone for the discomforts - both political and meteorological- of having to live in Missouri, who God himself has abandoned.