Totally agree Strategerist. More and more people of my generation are definitely seeing offspring as an economic burden. It is not an American phenomenon ...it is happening in any country that is starting to see wealth of some sort creeping in. For instance I am talking about my peers in Nairobi, Kenya, who have a job earning at least 150,000 US$ per year, in the early 30s, and all of us don't have kids ...apart from a couple here and there. Yet in the rural areas, and among the poor, many kids are very normal (until about a decade ago Kenya had one of the highest birthrates in the world).
As median incomes increase the number of children goes down as more and more people put off children until a 'more convenient' time. Add to these considerations the fact that a 'proper' education (which, in my circle, is taken as having the child in a high-class private school with an international curriculum) can be quite expensive (some of the upper-tier schools in Kenya, at Grade level, can be up to US$24,000 per year per child). Then there are lifestyle considerations ...the type of car you drive is very important, as is the location you live in. In a certain demographic living in an apartment would be looked down upon, thus people opt for stand-alone houses. This has made Nairobi (capital city of Kenya) and Mombasa (second city of Kenya) as the number 1 and 2 fastest growing prime real-estate markets in the world! (Talk about a bubble - see the following links: http://edition.cnn.com/2012/06/28/business/kenya-luxury-housing-boom/index.html and http://www.the-star.co.ke/news/article-23765/luxury-residential-market-startling)
What does all of this mean? That among the well-to-do children have become a low priority, with most who are having kids having one (at most two, with more than that being among the truly wealthy). Yet, in the lower income echelons, many kids still remain the rule.
There is also the rise of 'SINKs' and 'DINKs' (single income no kids, and dual income no kids) set-ups, where in the case of a DINK two professional people marry and decide to not have children as a way of enhancing lifestyle.
Thus, this is a phenomenon that is being seen everywhere in the world. From the developed world; to emerging markets like (upper income) India and (wealthier places of) Brazil; and now even in (wealthier segments) of frontier economies in Africa and Asia.
The critical issues may be many, but economics and the way people view necessities from a financial perspective (i.e. the child or the nice house in a nice location) is definitely one of the big ones. The way things look it appears that the tradition of having many children has been relegated to the poor (for the most part), and (at a lower level) to those who, out of personal choice, decide to have many children. Most people in both developed/developing economies simply do not see children in the same manner that prior generations saw them, and as you mentioned the shift away from an unmechanized agricultural society changed several societal rubrics that simply shifted how children are seen by the majority.
This is why, even in staunchly Catholic countries in (say) Latin America, birth control is a given. Going forward a lot of the population growth will be amongst the poor.
There is far more to declining birthrates than just money, the cultural factors I mentioned. At the same time as basic costs go up, so do cultural and government *expectations* of potential parents. And this can be both profound and discouraging.
Two generations ago, if children wanted to go to college, they would often as not work their way through, paying their own tuition. And importantly, tuition was paid up front. So when they graduated, they would be employable, but have little or no money to start with.
However, they also had no debt. What they earned, after taxes, was theirs, along with prospects for a long time job and promotions offering more money. They could timetable both marriage and children.
Today, to get through college, costs are so very high that most students assume very large debts, so when they graduate they do so “in the hole”. This translates to having to delay marriage *and children*, for years until they are “just broke”, “beginning their independent adult life” at 25 or even 30 years of age.
Since most people only have about a 20 year optimal window to have children, from 17 to 37, practically speaking only about 15 years, this tightens things up considerably.
Then other cultural and government factors come into play, such as demands on potential parents to provide a higher “quality of life” for their children. And this is not just money, but time and energy that is demanded of them.
Eventually it reached a point where having a child was a major burden, estimated cost a minimum of $100,000 for eighteen years, after both parents were debt free; having two children was much more difficult; having three or more almost out of the question.
Even with enough money, the demands of time and energy are such that “optimally” it would take four or five people to raise three or more children.