++Addition++See Jason Malloy's work in the comments.
"Have kids" wasn't exactly the right answer to the question of how one finds his way to happy happy village, though "don't have kids" doesn't get the peregrinator any closer, either. But happiness doesn't echo through time, it expires along with its bearer. A question of greater consequence is how we get people to have more (or fewer) children. Okay, it's obvious in a technical sense. But what about a behavioral one?
By way of ordinary least squares, here are the absolute multiple regression coefficients for eleven variables that may reasonably be assumed to have substantial predictive power in terms of realized fertility. For contemporary relevance and to avoid racial confounding, responses are from 2000 onward and only non-Hispanic whites are included. Asterisks indicate statistical significance at 95% confidence.
First, for men, with parenthetical indications of what is associated with greater fecundity:
Marital status -- .37* (marriage = procreation)
Age -- .33* (time = procreation)
Church attendance -- .10* (churchgoing = procreation)
Education -- .07* (less = procreation)
Number of female partners -- .04 (fewer = procreation)
Political orientation -- .03 (conservatism = procreation)
Social class -- .03 (lower = procreation)
IQ (wordsum) -- .01 (intelligence = procreation)
Income -- .01 (less = procreation)
Happiness -- .00 (no relationship)
Belief in God -- .00 (no relationship)
The older a person is, the more time he's had to have kids. Surely age is the strongest predictor of the number of children a man has sired, isn't it? False. Marital status is even more powerful than age is, at least for those with a y-chromosome. Despite rising illegitimacy and declining marriage rates, there is no better* way to get a man to spread his seed than to have him tie the knot. Churchgoing and school-avoiding also push a man towards fatherhood. Nothing else matters much--getting around hurts a smidgen, being conservative helps a bit, but these things only marginally so.
Tangentially, a note to those interested in this sort of stuff: Religious activity tends to be more important than stated religious belief is. Speaking in broad generalities, the man who believes in God but doesn't pray, worship, or otherwise do anything else meaningful as a consequence of that stated belief is behaviorally more similar to an atheist or an agnostic than to a pious person who can reliably be found in the pews on Sunday.
Age -- .32* (time = procreation)
Marital status -- .24* (marriage = procreation)
Education -- .18* (less = procreation)
Class -- .11* (lower = procreation)
Church attendance -- .07* (churchgoing = procreation)
Political orientation -- .06* (conservatism = procreation)
Belief in God -- .06 (belief = procreation)
IQ (wordsum) -- .04 (stupidity = procreation)
Income -- .02 (less = procreation)
Happiness -- .02 (unhappiness = procreation)
Number of male partners -- .01 (fewer = procreation)
The variables are a more even keel than they are among men, with the only three not mattering much being how much a woman gets around, how happy she is, and how much money she (or her partner) makes. Age is the biggest predictor, followed by marital status, education (a killer of kid creation in the Western world), and then social class, all of which are notably influential.
Affordable family formation (and expressive piety!) isn't just the route to a Republican resurgence, it's the pathway to procreation, too. Societally, of course, we're moving in the opposite direction, as marriage and religious attendance declines while years spent accumulating debt in school instead of creating value in the workforce is still the predominant advice proffered to American youth. Forty more years!
GSS variables used: YEAR(2000-2010), SEX, RACECEN1(1), MARITAL, AGE, EDUC, CLASS, ATTEND, POLVIEWS, GOD, WORDSUM, CONINC, HAPPY, NUMMEN, NUMWOMEN
* With the obligatory qualification that correlation does not necessarily prove causation and is in this context best thought of as merely suggestive.