Consider a childless couple with very different incomes, which usually yields a marriage bonus.

FORBES: Marriage, Children, Tax Credits, And The Alternative Minimum Tax

As a rule of thumb, economists reckon that a family with one child needs 30% more income than a childless couple to maintain the same living standard.

ECONOMIST: Most of the rich world is short of babies

He claimed that the unexplained money had come from a childless couple of Holocaust survivors, living in New York, who had adopted his wife, Yaffa, before they were married.

ECONOMIST: Israel

Beautiful and brown, the tiny creature lands next in a sleazy pawnshop, then in the cramped Prague apartment of a childless couple, dreamy Mila (Natasa Burger), who has wanted a baby desperately, and her rent-a-cop mate, Franta (Jiri Machacek), who can't adopt because of his criminal past as a soccer hooligan.

WSJ: Bouncing Czechs -- and Besieged Nazis