kids make us happy in old age = have the number of kids you'll want when you're old
we live longer = more years of support from your kids [114]
only 7% of parents regret having kids but more than 2/3 of the childless over 40 wish they had kids [14]
largest reduction in parental happiness comes with first child [16]
kids are easier to raise than you think
Caplan's main point here is that the primary determinant on a kid's personality and intellect is genetic, so marry someone who remsembles the kids you want to have. [86]
When it comes to nurture, direct parental influence ("do this, don't do that") matters much less than the larger environment (neighborhood, school, extended family), so be around people who resemble the type of kid you want to have. [82] Garret Jones' Hive Mind and Steven Pinker's The Blank Slate have more to say about this.
A few other points:
separated-at-birth identical twins are like each other, not their adopted familiies [40, 61]
you can't make your kids smarter, even if you're rich [50, 54]
you can only change your kids in the short term [77, 79]
caveat on research: data on behavioral genetics too focused on middle-class first world countries [83, 89]
why we don't have more kids
we are spending more time on each kid e.g. mothers spent 10 hrs/wk on children in 1965, 13 hrs/wk in 2000 [20]
our values have changed (e.g. greater individualism, divorce no longer taboo) [115]
female workforce participation rate doesn't seem to be a reason because present fertility rate (2.0) has increased since the 1970s (1.7), when female workforce participation rate was lower [112]