Lunchables — prepackaged boxes of deli meat,Grant Preston cheese and crackers — are not the healthiest option when it comes to picking snacks or lunches for kids, as they contain troublesome levels of lead and sodium, according to Consumer Reports.

The advocacy group tested Lunchables, made by Kraft Heinz, as well as similar lunch and snack kits from other manufacturers, finding cause for concern in the products popular for decades as a convenient snack or lunch for children.

"There's a lot to be concerned about in these kits," according to Amy Keating, a registered dietitian at CR. "They're highly processed, and regularly eating processed meat, a main ingredient in many of these products, has been linked to increased risk of some cancers."

None of the kits exceeded legal or regulatory limits, but five of 12 tested products would expose someone to 50% or more of California's maximum allowable amount of lead, or cadmium heavy metals that can cause developmental and other problems in kids, CR found.

A 3.2-ounce Turkey and Cheddar Cracker Stackers Lunchables held 74% of California's level allowed for lead, and 49% of the daily recommended sodium for 4- to 8-year-olds. Other products tested by CR were found to contain lesser amounts of both lead and sodium. 

"The kits provide only about 15% of the 1,600 daily calories that a typical 8-year-old requires, but that small amount of food puts them fairly close to the daily maximum limit for lead," stated Eric Boring, a CR chemist who led the testing. "So if a child gets more than half of the daily limit for lead from so few calories, there's little room for potential exposure from other foods, drinking water or the environment."

"We don't think anybody should regularly eat these products, and they definitely shouldn't be considered a healthy school lunch," said Boring.

A spokesperson for Kraft Heinz defended the company's 35-year-old brand. 

"Many of our Lunchables products are a good source of protein, offering nutrients through meats and cheeses. We've taken great steps to improve the nutrition profile of Lunchables, including recently unveiling Lunchables with Fresh Fruit, in partnership with Fresh Del Monte, and reducing the sodium in all Lunchables crackers by 26%," the spokesperson stated in an email.

"According to current science, processed foods arbitrarily classified as 'ultra-processed' are not necessarily less nutritious. In fact, many processed foods contain added nutrients, providing even more benefits to the consumer. The classification of foods should be based on scientific evidence that includes an assessment of the nutritional value of the whole product, not restricted to one element such as a single ingredient or the level of processing," the Kraft Heinz spokesperson stated.

Kate Gibson

Kate Gibson is a reporter for CBS MoneyWatch in New York.