I said unique, old people need a lot of health care, generally way more than a kid. Most kids after birth just have routine checkups and not much else. Infants might get a bit more doctor visits because the parents don't know if they should worry or not because the infant can't speak, but generally even those amount to nothing.

Babies more universally need diapers than old folks, and do eat more than an older person, but health care is absolutely bigger for elderly.

So you just said about 20 years of life is only twice that of the last three years of life for your starting figure. Add in college and it's still not that egregiously more.

You feel the need to add public school costs, but not add in medicare, social security, and other expenses exclusive to old age.

...uhh..... do you have ANY citation for those numbers?

Cost per child is $300k, $400k including college.

Only one in three Millennials have gone to college, so you'll need to pro-rate this. You're also talking about a population that begun employment between 14-17, even in an advanced economy like the US. So that cost is offset by revenue, especially in those later years.