They Grow Up So Fast

Consider what happened one spring evening at midnight in 1987: seven million American children suddenly disappeared. The worst kidnapping wave in history? Hardly. It was the night of April 15, and the Internal Revenue Service had just changed a rule. Instead of merely listing each dependent child, tax filers were now required to provide a Social Security number for each child. Suddenly, seven million children - children who had existed only as phantoms exemptions on the previous year's 1040 forms - vanished, representing about one in ten of all dependent children in the United States.

Source: Levitt, Steven D. and Stephen J. Dubner. Freakonomics: A Rogue Economist Explores the Hidden Side of Everything. Harper Collins: 2005.