Having kids is basically never going to cause someone to go from rich (excess wealth and luxury) to actually poor (struggling to survive).

However, it definitely can be enough to take someone who is just barely getting by, making their car payments, enough food on their plate, etc. to start to struggle. Kids are very expensive.

No-one is not having kids because they want a second yacht. But there are a lot of people who genuinely cannot afford to survive with a child.