Parents often worry about what they pack in their children's lunchboxes, but some of them may already carry hidden hazards inside. This summer, Wal-Mart, the nation's largest retailer, pulled some of them off the shelves fearing there may be lead in some of the vinyl liners.

Ask any parent and they'll tell you that finding the right lunchbox can be a challenge.

"The right color and the right style and they're fifth graders, so it's important. I mean that's a big thing. The right style and the right colors," said Kathy Charlton, parent.

"Whatever character, whatever color that kind of thing. Maybe if there's a water bottle in it or not," added Betsy Innis, parent.

But you may need to add safety to that list.

The Food and Drug Administration recently mailed letters to manufacturers, warning them about a potential health hazard, and urging them to refrain from marketing lunchboxes containing lead. The hazard is small, but the FDA determined it serious enough, to sound the alarm.

The concern is that the lead in some lunchboxes, could somehow leak into your child's food, specifically, lunchboxes with vinyl liners that contain what's called polyvinyl chloride, or PVC. Taking no chances, Wal-Mart voluntarily pulled those lunchboxes off store shelves.

"It never occurred to me that there would be something like that that might be of concern in a lunchbox," said Innis.

The Consumer Product Safety Commission regulates the handling of such products. It says there is no cause for concern. It tested a cross section of 60 lunchboxes for lead. The results showed consistently low levels. Levels so low, that the CPSC says the lunchboxes do not present a hazard.

Based on those tests, the CPSC says children would have to rub their lunch box and then lick their hands more than 600 times every day for 15 to 30 days in order for the lunch box to present a health hazard.

"It sounds as though there is a very trace amount of lead, if any, in these lunchbox liners, and so the odds of it becoming a real health hazard are low, but it's a question that remains for debate," said Pediatrician, Dr. Ari Brown. "We know that lead exposure can cause anemia, it can cause learning disabilities, and even more severe, life threatening issues."

The vinyl lunchboxes in question are still available in some stores.

"It's kind of scary because you're always trying to protect your kids in every way possible and that's just one more thing you have to worry about," said Charlton.

If you're still worried make sure all food is wrapped, or placed in sealed containers — or trade in your child's vinyl lunchbox for a brown paper bag.

The Consumer Product Safety Commission says it tested only soft vinyl lunchboxes. The group does not know whether hard plastic or metal lunch kits contain lead.