> effectively the janitor's wage has to go down to cover for the risk the software engineer has kids.

Salaries are usually not a zero-sum game.

Having kids is a full time job. When you get kids you can kiss all your free time goodbye, say goodnight to the side projects. Having kids is not good for your career, or other life goals. And if you are alone, eg. you have to pay for everything yourself, it also means a life in poverty.