They don't always. The Duggars are probably the most extreme counterexample; they live frugally given the number of mouths to feed, but Jim-Bob Duggar's worth about $3.5 million, and they have, what, 19 kids (and possibly still counting)? read more
On average, people with higher income and net worth have fewer children because: Kids cost. You don’t need any further proof of that than to see how the Pew Research Center classifies income brackets. A single person is considered “upper-income” for survey purposes at $66,000. A family of 5 needs $145,000 to be considered “upper-income”. read more
The cycle continues: Poorer parents have less time and fewer resources to invest in their children, which can leave children less prepared for school and work, which leads to lower earnings. American parents want similar things for their children, the Pew report and past research have found: for them to be healthy and happy, honest and ethical, caring and compassionate. read more
It's too costly for the rich to have children. Yet the poor can have many children due to subsidy. Just look at this: 'Feckless father' of 17 facing life in jail for murder - Telegraph A poor man can father 17 children. There. No body jailed him for being deadbeat. No women bother suing him for child support. read more