Child Field Workers: Who’s Picking Your Food?

“I grew up right here working on the tobacco farm and I certainly learned my work ethic from growing up on a farm,” he said. “I think we do have to have protections and oversight and transparency but I don’t know any farmers that want to employ 5-year-olds or 6-year-olds or 10-year-olds. Can it happen? Sure. And it can be legal provided they have the documentation, the written consent and record keeping of the birthdate.”

Wicker works with 750 farmers through the NCGA to provide small family farms with regulated migrant labor under the H2A visa program. He said labor issues in agriculture should be part of the public policy debate. (Read More: California Farm Labor Shortage 'Worst It's Been, Ever'.)

But CNBC’s investigation found few are willing to talk about the issue in public. The U.S. Department of Labor declined requests for an interview on the subject and calls to over a dozen produce companies in California were not returned.

The farmer who owns the tobacco field where our undercover investigation found children at work did talk, briefly. He first told CNBC that he has contracts to supply tobacco to Philip Morris International , Alliance One International and U.S. Tobacco Cooperative. However, he abruptly ended the phone call when asked about where he gets his workers.

In agriculture, it’s common to employ a farm labor contractor to supply the labor, which allows the grower to save money on workers’ compensation and other costs because the contractor is then responsible for adhering to labor regulations.

But Philip Morris International, one of the three companies that contracts with the farmer we contacted, sees the situation differently.

“In those situations where farmers do decide to use third party contractors, as far as we’re concerned the responsibility is still with the farmer to make sure that the child labor preventions and the other provisions in our contracts are enforced,” explained Anne Edwards, Director of External Communications for Philip Morris International.

Concerning CNBC’s investigation that exposed child workers, Edwards added, “Clearly this is something that we need to look into as a matter of urgency because this is just completely unacceptable.”

In an emailed response, Alliance One International told CNBC, “We take the situation that you identified very seriously and plan to thoroughly investigate the matter so that if child labor was being used by one of our growers or their third party contractors, an appropriate response, including further education is implemented.”

U.S. Tobacco Cooperative also responded via email, stating, “We condemn strongly any violation of state or federal labor laws.”

Though the system for enforcement is not perfect, NCGA’s Wicker said progress has been made by all responsible parties in the supply chain.

“The companies have stepped up big time, the manufacturers, the leaf dealers, have contracts that growers are required to comply with all federal, state, and local laws,” he said. “The contracts have gotten more specific in detail. I’d say over the last 6 or 7 years there’s explicit language about child labor, forced labor, complying with the law and keeping all the records, and undergoing safety training.”

NCGA also is in a multi-party stakeholder group working for fair labor practices in the agriculture supply chain along with manufacturers, non-governmental organizations, labor unions and government representatives, Wicker added.

“I’m not saying we’re perfect, we want to be perfect, we’re human beings so we’ll probably never be perfect, but we want to partner with the companies and with the workers and their representatives and talk about best practices,” he said.

—By CNBC's Sabrina Korber