Glenn Reynolds has a good editorial in the Wall Street Journal about the social costs of parenting. As a newlywed who is looking forward to having children (in a few years) I'm glad to hear that I'm not the only one who regrets that childrearing has become less appreciated in our culture.
There's also the decline in parental prestige over generations. My mother reports that when she was a newlywed (she married in 1959) you weren't seen as fully a member of the adult world until you had kids. Nowadays to have kids means something closer to an expulsion from the adult world. People in the suburbs buy SUVs instead of minivans not because they need the four-wheel-drive capabilities, but because the SUVs lack the minivan's close association with low-prestige activities like parenting, and instead provide the aura of high-prestige activities like whitewater kayaking. Why should kayaking be more prestigious than parenting? Because parenting isn't prestigious in our society. If it were, childless people would drive minivans just to partake of the aura.
In these sorts of ways, parenting has become more expensive in nonfinancial as well as financial terms. It takes up more time and emotional energy than it used to, and there's less reward in terms of social approbation. This is like a big social tax on parenting and, as we all know, when things are taxed we get less of them. Yes, people still have children, and some people even have big families. But at the margin, which is where change occurs, people are less likely to do things as they grow more expensive and less rewarded.
All that, in addition to parents' lessened ability to discipline and greater supervisory responsibility, has led to a cost/benefit analysis that results in fewer children, to the detriment of our society.