In my city of Seattle you simply cannot have more than one kid in your twenties. You simply do not have the income to pay the Seattle rent / mortgages and pay daycare for more than one kid at the start of your career. Forget about going to a concert or a restaurant: there is simply no money for it.

Young people in Seattle either live in studios or 1 bedroom apartments, or live with roommates, or with their parents. You cannot raise more than 1 kid this way.

This is the calculus me nu my wife did when we chose to have one kid only. Looking back and seeing how life progressed we made the right choice.

And yet I bet there are thousands of young people in Seattle having kids. These limits are all about what kind of life you want for yourself, and not about what is possible.