LATEST CENSUS DATA

• The population younger than 5 stood at 49.9 percent minority in 2012.

• The nonwhite population increased by 1.9 percent, to 116 million, or 37 percent. Hispanics make up 17 percent of the U.S.; blacks, 12.3 percent; Asians, 5 percent; and multiracial Americans, 2.4 percent.

• About 353 of the nation’s 3,143 counties, or 11 percent, are now “majority-minority,” including six that tipped last year.

• Among the under-5 age group, 22 percent live in poverty, typically in more rural states such as Mississippi, Arkansas and Louisiana. Black toddlers were most likely to be poor, at 41 percent, followed by Hispanics at 32 percent and whites at 13 percent. Asian toddlers had a poverty rate of 11 percent.

In a first, America’s racial and ethnic minorities now make up about half of the under-5 age group, reflecting sweeping changes by race and class among young people. Due to an aging population, non-Hispanic whites last year recorded more deaths than births.

These two milestones, revealed in 2012 census estimates released Thursday, are the latest signs of a historic shift in which whites will become a minority within a generation, by 2043. They come after the Census Bureau reported last year that whites had fallen to a minority among newborns.

Fueled by immigration and high rates of birth, particularly among Hispanics, racial and ethnic minorities are growing more rapidly in numbers than whites. The decline in the U.S. white population has been occurring more quickly than expected, resulting in the first “natural decrease” — deaths exceeding births — for whites in more than a century, census data show. For now, the non-Hispanic white population continues to increase slightly, but only because of immigration from Europe.

Based on current rates of growth, whites in the under-5 group are expected to fall below 50 percent this year or next, said Thomas Mesenbourg, the Census Bureau’s acting director.

“This is the tipping point presaging the gradual decline of the white population, which will be a signature demographic trend of this century,” said William H. Frey, a demographer at the Brookings Institution. “More so than ever, we need to recognize the importance of young minorities for the growth and vitality of our labor force and economy.”

The imminent tip to a white minority among young children adds a racial dimension to government spending on early childhood education, such as President Barack Obama’s proposal to significantly expand pre-K for lower-income families. The nation’s demographic changes are already stirring discussion as to whether some civil rights-era programs, such as affirmative action in college admissions, should be retooled to focus more on income than on race and ethnicity. The Supreme Court will rule on the issue this month.

The government projects that in five years, minorities will make up more than half of children under 18.

Studies show that gaps in achievement by both race and class begin long before college, suggesting that however the high court rules, the U.S. remedies to foster equal opportunity will need to reach earlier into a child’s life.

“The educational system is likely to be the most widely used and most acceptable policy tool we have for equalizing life chances. But it does not seem so far to achieve this goal,” said Timothy Smeeding, an economics professor at the University of Wisconsin-Madison who specializes in income inequality. “This specter of unequal opportunity may be the biggest negative social outcome of the continuing American inequality boom.”

The gap between rich and poor in the U.S. has now stretched to its widest since 1970, making opportunities to reach the middle class increasingly difficult.

Longer-term changes in family structure, such as a decline in marriage, have led to a rise in single-mother households across all racial groups, with the fastest growth now occurring among whites. More than 40 percent of newborns are now born out of wedlock in low-income families.

Smeeding’s analysis of the latest research and data on social mobility shows that a child’s achievement varies widely depending on a parent’s education and income. The reason: More educated parents tend to have fewer children and generally earn more money, allowing them to spend larger amounts of time or money on a child’s development.