ST. LOUIS — For Roxana and Miguel Boland, the decision for her to stay at home and care for their young son was an easy one.

As an immigrant from Mexico, she wanted to follow a tradition that is steeped in Hispanic culture: Mom stays at home with the children and Dad is the breadwinner.

The Bolands of University City are far from alone in those defined roles. In the most comprehensive look yet at the more than 5 million stay-at-home mothers across the United States, the U.S. Census Bureau reports today that stay-at-home moms tend to be younger than mothers who work outside of the home and that they are more likely to be Hispanic and to have been born in a foreign country.

A higher percentage of stay-at-home moms have preschoolers in the household, compared to other mothers. And stay-at-home moms tend to have less education than mothers who have paying jobs.

The authors of the Census Bureau report, which takes a wide look at the makeup of American families, admit they were caught off guard by the stay-at-home mom findings.

"There's been lots of talk in the press about those highly educated with high-earning positions opting out of the labor force to stay at home with their children," said Census Bureau family demographer Diana B. Elliott, who co-authored "America's Families and Living Arrangements" based on 2007 information.

"But when we actually ran the tables, we saw that with this nationally representative sample, that it's really mothers who have less than a high school education, women who are younger."

The results of the study come from a sampling of 3 million households across the country. A stay-at-home mom is defined by the Census Bureau as a woman who has a child under the age of 15 and has been out of the work force for a year while her spouse has been working continuously during the same year. Under that definition, stay-at-home moms represent about 24 percent of mothers. Women who earn income from a job from home do not fit the description.

Luis H. Zayas, director of the Center for Latino Family Research at Washington University's Brown School of Social Work, said it may not make economic sense for less-educated women to take low-paying jobs when factoring in the cost of child care, especially if they are recent immigrants.

"Overlaying the economic reasons, there is the issue of culture," he said. "The role of mother is about being very much devoted to your children." In fact, he said, "the cultural ideal of a Hispanic woman is as a mother who has her attention to her children. She maintains a great proximity to her kids."

Roxana Boland said she and her husband didn't even consider what is now commonplace in the U.S.: both parents in the labor force.

"It was never a question. We don't come from that culture," said Boland, 31. "I think if you can stay at home, why not?"

Mothers' choices involving work outside the home have been long debated, as women weigh the benefits of more household income and possible financial stability against the need for more time with children during their developing years.

Women cite various reasons for staying home. They argue that no one can give more attention, love and guidance to a child than a parent. Mothers who stay at home say it gives them the flexibility to be more involved in their children's activities, such a volunteering at school. And stay-at-home moms say having a parent present creates a more relaxed and flexible schedule for the entire family.

Census Bureau estimates from 2007 show that 61.5 percent of households have two parents working. Illinois mirrors the national level, but Missouri shows a higher percentage of two-income families, at 68.5 percent.

The number of stay-at-home moms has risen to 5.3 million in 2008, from 4.5 million in 1994. The 17 percent increase matches the overall increase in total population during the same time frame. By contrast, there were 140,000 stay-at-home dads in 2008, up from 76,000 in 1994.

Despite such growth, the total number of stay-at-home parents dipped slightly in both categories in 2008. The Census Bureau attributes that to the recession and a stay-at-home parent getting a job to offset the job loss of a spouse. Labor experts point to December 2007 as the beginning of the recession.

Najia Bari, 31, of Chesterfield, emigrated from Pakistan soon after she got married in her early 20s. When her first child was born eight years ago, she knew she wanted to be a stay-at-home mom.

"I saw my grandmother and my mother do the same thing, and it influenced me," she said.

It's gratifying for her own mother to see how her children have become successful adults, she said. Recently, both of Bari's children have started school full time, and she has started a part-time course in respiratory therapy.

But, even when she completes the program, she says, she only wants to work during the hours that her children are in school.

"I have to be home with them. I want to pick them up from school" and be there when they get home, Bari said.

At least, "until they go to college and are grown up."