Thousands of children, many too young to drive, are hard at work putting in long hours in brutal conditions to make sure the rest of us eat well -- and cheaply.

NBC Bay Area’s Investigative Unit spent weeks penetrating the close-knit and tight-lipped community of migrant workers and found dozens of children working the fields in the San Joaquin and Sacramento valleys – some who started work at 11-, 10- and even 8-years of age.

While an 8-year-old could not work in an office or fast-food restaurant, a 1938 law allows them to legally work in agriculture.

[Click here for behind-the-scenes photos of the reporting and production of this investigative series.]

These children are working a full day in the fields picking, trimming and cultivating fresh fruits and vegetables. They often work 9 to10 hours a day in 100-degree-plus heat.

NBC Bay Area’s Investigative Unit found these children working all over -- not in China, not in Indonesia, not in Guatemala, not in Mexico - but in the United States, from North Carolina to California. Everyone interviewed worked on a large farm, not a small, family one.

And these, for the most part, are not illegal immigrants, but children born here in the United States.

[Click here to see when and and what age certain children can work.]

A typical day in one Central Valley migrant labor camp starts at 4:30 a.m.

Among those workers is a 15-year-old boy, whom we will call Ralph, who joins dozens of other young people heading to work. Some of them were told by direct supervisors to lie about their ages in order to get past the “bosses” in order to work.

During Ralph’s work day, it reaches 106 degrees.

“We get tired and like we get kind of tired and our arms hurt,” Ralph said, adding this is the second year he has worked in the fields full time. “It is too hard to be in the fields.”

United States labor law, which dates back to 1938, allows children 12 years old, and depending on the circumstances, even younger, to legally work in agriculture.

Click here to read the Fair Labor Standards Act of 1938 and the US Department of Labor’s summary of exceptions for agriculture.

NBC Bay Area found dozens of other children like Ralph.

“Like seven years, since I was 8 years old until now,” one 15-year-old said, describing when he started in the fields.

Another of the young workers said, “I was in 6th grade. I was 11.”

Yet another young girl described working so hard when she was 11 that her fingers bled.

“I had to carry a box and I had cuts on my fingers,” she said. “I came out (of the fields) really tired, it was really hot and I didn’t really like it but it was worth it to go help my mom.”

[Click here to read the Fair Labor Standards Act of 1938.]

Certain crops are harder to pick for the children than others.

“Well, right now it’s tomatoes,” a teenager said. “It’s the hardest thing I’ve done. I have to like (work hard), bending over, standing up, carrying the buckets and throwing them.”

The hard work and long hours has some parents doing everything they can to keep their kids away from the fields, even though their families badly need the money.

“She (mom) doesn’t want to see me work there (in the fields),” said a girl we’ll call Carmen. That's why Carmen's mother forces her to stay in school away from the fields. “She says because it’s a lot of work,” Carmen explained. “She doesn’t want me to go through what she goes through (in the fields). She says it’s really painful, hard work. Every night I massage her back so that she can feel better in the morning.”

Carmen vowed to go to college and get a higher paying job so she can support her mother and get her out of the fields.

“I told her that when I get older I’m going to buy her a house and stop her from working,” Carmen said.

Carmen is not alone in her dreams. Everyone interviewed said they hope the money they earn will help them break out of this cycle and live a better life.

“Right now I want to be like an artist, like drawing,” said one teenager.

Critics of current U.S. labor law say these childhood dreams are jeopardized by a relentless cycle where young workers drop out of school to follow their families and the crops for work and then remain stuck in the fields because the children never finish their high school education.

“Children can work at any age on a small farm with their parents’ permission. It’s absolutely legal for a small farmer to hire a 6-year-old to pick blueberries,” said Zama Coursen-Neff of Human Rights Watch. Coursen-Neff authored a 2010 report that found child labor prevalent in fields across the United States.

Coursen-Neff added as unfortunate as it may seem, these long hours in the fields are perfectly legal.

“You have to realize that many children who are working in hazardous conditions in the United States are working absolutely legally because U.S. child labor law which is pretty good has a big gaping hole in it when it comes to agriculture,” Coursen-Neff said.

“Children are working in American fields at far younger ages for far longer hours and in far more hazardous conditions than all other working children in America,” Coursen-Neff said. “(Under current law) a child can work again for hire at age 12 on any size farm. And at age 14 they can work for hire even without their parents’ permission. A child of any age can work unlimited hours outside of school in agriculture even though in all other forms of work the number of hours that they can work is limited to make sure that they can get an education and to make sure that they’re not put at risk.”

Coursen-Neff said her research shows that low wages for migrant workers throughout the industry means these families need more workers in the field to make ends meet. It becomes an economic necessity that continues for generations.

NBC Bay Area’s Investigative Unit found those exact circumstances during the team’s weeks in the fields.

Another group that hopes to change this practice is the Association of Farmworker Opportunity Programs (AFOP) based in Washington, D.C.

“These kids know that there is a necessity in their family to be able to make ends meet, to be able to put food on the table and are out there in those fields trying to make that happen,” said Norma Flores Lopez, director of the AFOP’s Children in the Fields Campaign.

“The Fair Labor Standards Act of 1938 made two separate sets of rules,” said Flores Lopez. “There is a set of rules that covers children working in every other industry and then there is a separate set of rules for kids working in agriculture.”

As for the scope of the problem, Flores Lopez said there are many more children working in America at far younger ages than most of us might imagine.

“It is very difficult to be able to pin exactly how many children are out there because there is not a whole lot of data that is being collected by the government on this,” Flores Lopez saud. “But from our best estimates that we have been able to get we know that there is anywhere from 400,000 children to up to as many as 500,000 kids.”

Those kids, picking everything from grapes to almonds, all said they are laboring so long and so hard out of pure economics. The reality is that their parents simply can’t make enough money working the fields without their children's help.

One 15-year-old worker’s mother put it plainly: “With just my husband’s salary it’s not enough. The two of them need to work in order to have anything and to keep up,” she said through an Spanish interpreter.

Just this year, the United States Department of Labor tried to change the law and further restrict and even prohibit some children from working in fields.

But they met opposition from growers.

[Click here to read the proposed rules changes from the Federal Register.]

“What they were proposing was a little too strong a little too restrictive,” said second-generation grower Pete Aeillo of Gilroy, a critic of the proposed reform. “I think that the current (agriculture labor) regulations as they are I think are good I think they are sound. I think it’s OK for kids that young to be working (in the fields.) (It depends) now on how many hours that they work.”

Aiello and his family have owned and run Uesugi Farms, Inc. for decades, growing chilies, pumpkins, Napa cabbage and other vegetables on their property off Highway 25 south of Gilroy.

Uesugi employs 180 on its direct payroll and between 500 and 600 seasonal contract workers, mostly during the harvest season.

After other critics lodged similar complaints in Washington, the Labor Department withdrew the proposed new rules in April. Critics also said the proposed rules as drawn up by the Labor Department would have hurt family farms although department officials dispute that.

But even Aiello admitted there are some fellow growers who look the other way and employ children who are 12 and younger.

“I know it does happen,” Aiello said. “And that’s unfortunate.” On July 24, the U.S. House of Representatives passed, by a voice vote, House Resolution 4157, a bill designed to prevent the Department of Labor from even attempting to change the labor law regarding children in agriculture in the near future.

Proponents of the bill say the proposed Department of Labor rules would hurt family farms and 4-H clubs.

Only one representative, U.S. Representative Lynn Woosley, a Democrat from Sonoma and Marin Counties, spoke out on the House floor against this legislation. Similar legislation has been proposed and awaits action in the U.S. Senate.

[Click here to read HR 4157, the bill that passed the US House of Representatives on July 24, 2012.]

What most sides can agree on is that this issue is largely unknown.

“I don’t think they (Americans) do (realize children are picking their food),” Aeillo said. “I think Americans are largely clueless about the labor in general that supplies their food. And whether it’s their age or their ethnicity or their legal status or any of the above I think Americans are in the dark about what’s going on.”

The NBC Bay Area Investigative Unit reached out to a dozen other different large grower organizations as well as large food processors and producers to get their views on both the issue of child labor in America and the U.S. Department of Labor’s proposed rules changes governing child labor in agriculture.

They either e-mailed us refusing comment or did not return phone calls or e-mails requesting comment.

In a statement California's Farm Bureau Federation said, "If there are children working on California farms in violation of the law, that is an illegal activity that should be reported to the state labor commissioner. The California Farm Bureau Federation and other farm organizations work with our members to help them comply with all labor laws."

[The full statement is available here.]

NBC Bay Area’s Investigative Unit also asked U.S. Secretary of Labor, Hilda Solis, who was in the San Jose-based NBC Bay Area studios in late July, to sit down and talk on camera about child labor and the proposed rule changes that her department withdrew in April.

Solis’ staff declined our requests for us to talk about child labor in agriculture saying her schedule was too busy.

(Editor’s note: To protect the minors and families in this story from retribution, we changed the names of the teenagers we talked with about this issue. We also are withholding their locations.)