Tens of millions of American children are among the recipients of food stamps, according to a new report that casts light on who benefits from the program that has been the subject of heated political debate.

The annual report from the United States Department of Agriculture showed that about 45 percent of food stamp benefits went to children under 18, totaling about 20 million youngsters. Nine percent of recipients were age 60 or older, and nearly 10 percent were disabled adults who were under 60, according to the analysis of food stamp usage for the fiscal year that ended in September 2012. The total cost of the program in the 2012 fiscal year was $78.4 billion, which has raised concerns among some lawmakers that costs are growing out of hand. But economists said that doesn't take into account the toll it would take if the benefits were cut sharply, as some have proposed.

"The vast majority of these benefits go to people who, you know, we don't expect them to go out and work themselves," said Diane Schanzenbach, an associate professor of human development and social policy at Northwestern University.

A sign painted on top of a mural says 'We accept food stamps,' in Harvey, Ill. About 45 percent of food stamp benefits went to children under 18 in 2013. Melanie Stetson Freeman | The Christian Science Monitor | Getty Images

And in the many cases in which the benefits do go to households in which at least one person has a job, experts say it often means the family is not making enough money to feed children without extra help from the government. About four in 10 SNAP recipients live in a household in which at least one person had earnings, the new report found.

"While people may be working, they're working in jobs (in which) wages are not keeping up with inflation," said James Ziliak, director of the Center of Poverty Research at the University of Kentucky.

In recent years, experts say, many people also have turned to the food stamp program because of a short-term job loss or cut in hours. That's a temporary safety net the program is supposed to provide.

(Read more: For love and money: Many parents want to work) "There's a whole host of reasons why the parent may be having financial difficulty caring for the child, and I think the Great Recession … was a clear example of that," Ziliack said.

The vast majority of these benefits go to people who, you know, we don’t expect them to go out and work themselves. Diane Schanzenbach Associate professor of human development and social policy at Northwestern University

Participation in the SNAP program increased sharply after the nation went into recession in late 2007, and unemployment soared. Even as the economy has entered a tepid recovery, food stamp participation has been slow to subside.

About 46.6 million people, or around 1 in 7 Americans, received SNAP benefits in an average month during the 2012 fiscal year, the USDA report found. That's about the same amount of people who were using the program in December 2013, according to the USDA's most recent monthly data. "We know that there continues to be need despite the end of the Great Recession," said Craig Gundersen, a professor of agricultural and consumer economics at the University of Illinois.

The food insecurity rate—or the percentage of American households who had trouble feeding their families at some point during the year—rose sharply in 2008 and has not come down substantially since. About 14.5 percent of American households experienced food insecurity in 2012, according to the most recent government data. High cost and high-profile critics The swelling costs of the food stamp program prompted some lawmakers to call for drastic cuts as part of the most recent farm bill negotiations. In the end, Congress approved a bill that included a much less drastic cut of about $8 billion over 10 years, due to a change in how home heating assistance can be used to trigger an increase in benefits.

The new farm bill also clarifies some rules for eligibility and makes other changes, such as improving access to healthy food options.

Separately, most recipients saw their benefits reduced late last year, after a recession-era boost in SNAP payments expired. Some lawmakers remain critical of the program. An extensive report on poverty, released by the House Budget Committee chaired by Republican Rep. Paul Ryan, argued that SNAP has only modest benefits and discourages work. Earlier this year, Ryan told NBC News that he thought the War on Poverty had "failed." Benefits for children The food stamp program also often comes under fire from critics who say that people collect benefits they don't really need, or use it to buy food that's not healthy. (Read more: Seesaw economy: Nearly 1 in 3 dipped into poverty )