For the first time in U.S. history, whites of European ancestry account for less than half of newborn children, marking a demographic tipping point that is already changing the nation's politics, economy and workforce.

Among the roughly four million children born in the U.S. between July 2010 and July 2011, 50.4% belonged to a racial or ethnic group that in previous generations would have classified them as minorities, up from 48.6% in the same period two years earlier, the Census Bureau said Thursday....