Basic microeconomics recommends a simple strategy. Have the number of children that maximizes average utility over your whole lifespan. When you are 30, you might feel like two children is plenty. But once you are 60, you are more likely to prefer ten sons and daughters to keep you company and keep the grandkids coming.
I think there is a more obvious approach to the problem. Why not just have a market for children so parents can buy and sell them at various times to maximize utility at every given point?Um, he's joking, you do get that, right? Here I was, thinking we had an overpopulation problem what with shrinking resources and such. But apparently:
...adding people produces more GDP too (i.e., you increase the numerator as well as the denominator), and the not-so-obvious fact that some types of products (e.g., cures for rare diseases, music only a smaller percentage of people like) are profitable only when there is a large enough total population that the small percentage of people who benefit large enough to make the product worthwhile.