Venus Perez, 3, stands in line with her mother Criseira Perez as she waits to check in for an appointment May 16 at Mary's Center in Washington.A new census report shows a drop in white (non-Hispanic) births to below 50 percent. (Nikki Kahn/THE WASHINGTON POST)

For the first time in U.S. history, most of the nation’s babies are members of minority groups, according to new census figures that signal the dawn of an era in which whites no longer will be in the majority.

Population estimates show that 50.4 percent of children younger than 1 last year were Hispanic, black, Asian American or in other minority groups. That’s almost a full percentage point higher than the 49.5 percent of minority babies counted when the decennial census was taken in April 2010. Census Bureau demographers said the tipping point came three months later, in July.

The latest estimates, which gauge changes since the last census, are a reflection of an immigration wave that began four decades ago. The transformation of the country’s racial and ethnic makeup has gathered steam as the white population grows collectively older, especially compared with Hispanics.

The census has forecast that non-Hispanic whites will be outnumbered in the United States by 2042, and social scientists consider that current status among infants a harbinger of the change.

“This is a watershed moment,” said Andrew Cherlin, a sociologist at Johns Hopkins University who specializes in family issues. “It shows us how multicultural we’ve become.”

Although minorities make up about 37 percent of the U.S. population, the District and four states are majority minority — California, Hawaii, New Mexico and Texas.

Metropolitan Washington, where whites are in the minority, is far ahead of the curve. Among children younger than 5, there are more minorities than whites in virtually every jurisdiction except Arlington and Loudoun counties. Statewide, Virginia has just barely more white children under age 1 than minorities, but they are on the verge of falling below half.

One of the biggest factors in the demographic change is age. Whites are by far the oldest group. Their median age is over 42, so many are beyond their prime childbearing years. In contrast, the median age for Hispanics is under 28. Blacks and Asians have median ages in their early 30s.

As the number of white women in their 20s and 30s declined over the past decade, the number of white children dropped in most states, said Kenneth Johnson, a sociologist with the University of New Hampshire.

“The population is literally changing before us, with the youngest replacing the oldest,” he said. “This is the first tipping point. The kids are in the vanguard of the change that’s coming.”

Places that serve Hispanic mothers and children are experiencing a baby boom. Mary’s Center, which started in Adams Morgan in 1988 to provide immigrant women with prenatal care, opened its fifth center Wednesday in Adelphi.

“The people who migrate are the young and healthy people,” said Maria Gomez, founder of the center. “They are fertile, and that’s the cycle of life.”

Dozens of women who are pregnant or pushing strollers streamed into Mary’s Center on Georgia Avenue on Wednesday to see doctors or social workers. Fourteen toddlers listened to stories narrated in English and Spanish while their parents attended English lessons.

“There are a lot of kids now, and many of them are Latinos,” said Mayra Jacinto, a native of Guatemala who arrived two hours before her doctor’s appointment, holding her 5-month-old daughter, Ivonne.

In the short term, it’s not clear whether the baby boom will continue. Immigration from Mexico, the country of origin for the vast majority of Hispanic immigrants in the United States, has come to a standstill and may be moving in reverse.

William Frey, a demographer with the Brookings Institution, said the slowdown in immigration may delay the nation’s transformation to a majority-minority society from 2042 to 2050 or beyond. But he said it will not prevent it.

“Eventually, when the economy returns, we’re going to get more immigrants, maybe not from Mexico but from other parts of the world,” he said. Without so many youthful immigrants, he added, the United States would look more like Japan, with its disproportionate share of elderly citizens.

“We were already seeing a declining youth population in large parts of the country,” Frey said. “Without immigrants, we’d be essentially youthless. We had a perfect storm. We got them all coming, younger immigrants having children, at a time when we really needed them.”

The future is here, in Northern Virginia, where several hundred thousand immigrants have settled over the past 25 years from societies as different as Vietnam, El Salvador, Ethiopia and Iraq.

The backgrounds of children enrolled in Head Start programs in the area have changed with each wave of immigrants. From 2010 to 2011, Hispanics held steady, but the number of children of Asian and African origin jumped more than 30 percent, while those with roots elsewhere, such as from the Middle East, doubled.

“The face of Head Start here has changed, but not the earnest desire of these families to see their children do the best they can,” said Melinda Langford, the Arlington Head Start director for Northern Virginia Family Service, a private nonprofit agency that serves 2,400 children younger than 11.

At Langford’s program, six in 10 preschoolers have parents who were born in another country. Colorful drawings line the halls and classroom walls, signed with names such as Francisco, Dayana, Khadija, Ureal, Lavand, Betel, Estefany, Brittany and Seid.

Program officials describe their mission as an affirmation of diversity as well as an educational boost for struggling kids. Sometimes they face cultural challenges, such as parents accustomed to disciplining their children more harshly than U.S. laws allow. To help with communication, Head Start employs class assistants and family advocates who are native speakers of a wide range of languages.

Cherlin said the immigrant baby boom will eventually taper off. Studies suggest that the children and grandchildren of the newest immigrants will have birthrates much closer to those of non-Hispanic whites.

“The changes to the country may not be as huge as some people think,” he said. “Immigrants will change our society, but our society will change the immigrants.”

The new census estimates also offered a glimpse of a region that reflects national trends and in some cases defies them.

The District continued its rebound, attracting 16,000 new residents from all age groups — in one year gaining almost as many people as the 20,000 it added the entire previous decade. Although the number of African Americans rose by more than 2,000, their proportion dipped below 50 percent for the first time in decades. Whites had the biggest increase, at 8,000. But among babies, the number of Hispanic infants rose the most as a percentage, up 70 percent, to 1,700. The number of infants who are white also rose sharply, while there were fewer African American babies.

In both Maryland and Virginia, the numbers of Hispanics and Asians continued to grow sharply. The number of blacks increased modestly, while the number of whites was virtually unchanged.

In Prince George’s County, one of the most affluent majority-black counties in the nation, the number of African Americans declined slightly, while Hispanics and whites gained.

Staff writers Pamela Constable and Luz Lazo contributed to this report.