Children are astronomically expensive. Most working class and middle class parents cannot envision affording a second child so they have just one.
Well, the only really expensive thing is daycare. I'm afraid there's no ready solution to that - unless we're willing to get back to the idea of extended family and village to raise a kid. PS. I have three kids, I know what I'm talking about.
But yes, next to those three things most other expenses aren't that bad, or are avoidable with little down-side. Only other notable one's probably consumables (diapers, food, that sort of thing) which doesn't come close to any of the other three. Toys and clothes are practically free, if you're not picky. People get all kinds of expensive crap at baby showers, but very little of it's actually of much use, and most of the rest could have been had used for next to nothing.