Second of all: child tax credits agogo!
Malthus and macroeconomics provide only a partial picture of the deeper motives for the trend.
I believe the biggest motive is Yuppie self-absorption promoted by rampant materialism, unchecked by spirituality. Why bother to have babies when the prospect exists for almost indefinite life extension? Hence the spiraling market for nutritional supplements, personal care products and services, and rejuvenation treatments.
Watch for renewed worries about a First World population explosion of oldsters after medical investigations of immortality-promoting drugs begin to bear fruit within the next fifty years.
Whole new sets of questions about the absolute and relative values of life, innovation, economics and wealth distribution caused by these "advancements" will make today's arguments look like sandbox warfare.