With back-to-school drawing near, your kids are likely lobbying for a new backpack or the hottest sneakers.

But health officials say you shouldn’t overlook an important staple of their daily school life: a well-insulated, properly packed healthy lunch.

Keeping an eye on the weather and being mindful that what you pack for school lunch—and how you pack it—could make a big difference in your child’s health.

“I worry that families are not as educated as they should be about how they’re packing those lunches,” says Dallas dietitian Graciela H. Sanchez. “As parents, we’re just not as conscious of bacteria growth.”

Researchers at the University of Texas at Austin recently studied the sack lunches of 700 preschoolers in nine Texas childcare centers and found that 90% of them were kept at unsafe temperatures.

Of the lunches studied, 45 percent contained at least one ice pack. But 39% contained no ice pack at all. And even of those with at least one cold pack, 88% were at room temperature by lunch time.

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Nutritionists say that the best storage temperature is below 40 degrees Fahrenheit for cold foods and above 140 degrees for hot foods.

Not keeping food at the proper temperature puts your kids at risk for salmonella and E. coli, Sanchez says.

“If we rush to take things off the grocery shelf for E. coli why aren’t we being more careful at home?” she questions. “There are tricky things about bacteria: You can’t see or smell it, but you can still get sick.”

Sanchez says that some perishable foods—meats, cheeses and dairy products, such as yogurt—should simply be left out of lunch boxes when the weather is warm.

She also recommends using several cold backs in lunches and regularly washing lunch boxes and thermoses with hot soapy water. If lunch kits are fabric, soak them in the sink or throw them in the washing machine.

“Do some shopping around for a good lunch box,” she advises. “You need a well-insulated bag. The good ones are worth the money.”

And what if your child loves a turkey and cheese sandwich in her lunchbox?

Sanchez advises surrounding the food with cold packs to keep the sandwich chilled or considering one of these healthy—but not as perishable—lunch options:

  • Peanut butter or almond butter
  • Whole grain crackers
  • Hummus and carrots or other veggies
  • Dried fruit
  • Low-sugar granola bars
  • Whole fruit or fruit cups

Your child’s tummy, your child’s daycare or school, and you will be glad you did.