A small sample size, but all of my kids which go to a pretty high-end daycare seem to have a bit leg up on peers who have stayed home in terms of social skills, language, reasoning, and reading. That's not just me acting like my kids are the best (of course they are), that's those other parents mentioning it to me.

It's practically a college tuition per kid at age 0 though.

It does when the biggest expenditure category is for a positional good (ie. rent). There's only so much land in new york and so many apartment units. Being in a wealthy country means your peers are also wealthy, which means a household with double income can easily outbid a household with a single income.