The Duggar family just had their 17th child. They are very well off and debt free. What? Let's tell you a couple of facts about ther family. They live in a 7000 sq ft home, which by any reasonable standards is large.
But how do they afford a huge home and no debt? Well the father Jim Bob Duggar was previously a US state congressman. So he was earning over $158k/year in say 2004, and they live in Arkansas. Which most can assume is a pretty reasonable cost of living. However he currently is self-employed insurance salesman, and one could logically conclude he did not leave for a lower paying job. Hence supporting a family approximate 4x the median salary seems more reasonable.
But also realize their oldest child is only 19 and they have not yet started to pay for college. This could be a deciding factor in whether or not they stay debt free and are able to retire. It was previously mentioned that they did not achieve debt free status until child #12. This is still an amazing feat.
Well I guess if you want a lot of kids, make sure you make a great income. And try to be debt free.