Wal-Mart and two other top retailers said Friday they are suspending business with a large southwestern Michigan blueberry grower after investigators found children as young as 6 working in the grower's fields.

Wal-Mart, Kroger and Meijer said pending further information, they have stopped buying products from Adkin Blue Ribbon Blueberry Co. near South Haven, about 85 miles northeast of Chicago.

Adkin general manager Tony Marr said the company has a strictly enforced written policy prohibiting young children from working in its fields. All adult employees must sign copies of the policy, and the farm keeps the signed copies on file, he said.

"We certainly don't condone or promote child labor here in any way," Marr said.

The company has eight full-time employees and hires about 350 seasonal workers each year to harvest and process the blueberries grown on its 640 acres. About one-third of its berries are processed for sale as fresh produce and the rest are frozen for commercial use.

Adkin is conducting its own investigation to determine what happened, he said. Parents sometimes bring children with them because they don't have child care, he added.

"Wal-Mart, Kroger and Meijer are very large customers of ours, and certainly we're cooperating with them in providing information about our internal investigation, trying to figure out what the kids were doing there," Marr said.

The U.S. Department of Labor announced this week that a check of 35 randomly selected farms in Michigan led to eight being fined about $36,000 in all for violating federal migrant-housing and child-labor laws.

Ten other farms were cited for violations but not fined. Adkin was the lone farm fined for both migrant-housing and child-labor law violations and paid more than $5,500 in penalties, said Scott Allen, a department spokesman based in Chicago.

Wal-Mart Stores Inc. spokeswoman Caren Epstein said the Bentonville, Ark.-based retailer learned of the problem after being contacted by ABC News. Wal-Mart will not buy anything from Adkin "pending the outcome of an investigation by our ethical sourcing team," Epstein wrote in an e-mail.

Representatives of Cincinnati-based Kroger Co. and Grand Rapids-based Meijer Inc. made similar statements.

Thomas K. Thornburg, co-managing attorney of Farmworker Legal Services, said labor law violations are rampant among farms that use migrant workers.

"This isn't one abusive employer," he said.

Federal law does not allow children younger than 12 to work on farms. Children who are 12 or 13 can have nonhazardous farm jobs outside of school hours if they work on the same farm as their parents or with written parental consent.

Labor Department investigators found four children working in Adkin's fields during an unannounced visit on July 8. At least two of the children were under 12, including the 6-year-old.

Michigan is the nation's largest blueberry producer, with 110 million pounds harvested in 2008.

During inspections throughout the state, investigators found migrant workers living in unlicensed migrant labor camps with sewage from a faulty septic system seeping up near living units. They also discovered untreated waste water spilling out of broken pipes, no hot water for hand washing and infestations of bugs and rodents.