For the first time, racial and ethnic minorities make up more than half the children born in the U.S., capping decades of heady immigration growth that is now slowing.

New 2011 census estimates highlight a historic shift underway in the nation's racial makeup. They mark a transformation in a country once dominated by whites and bitterly divided over slavery and civil rights, even as it wrestles now over the question of restricting immigration.

"This is an important landmark," said Roderick Harrison, a former chief of racial statistics at the Census Bureau who is now a sociologist at Howard University. "This generation is growing up much more accustomed to diversity than its elders."

The report comes as the Supreme Court prepares to rule on the legality of Arizona's strict immigration law. Many states are weighing similar get-tough measures as fewer Hispanics are opting to enter the U.S. due to the weak economy.