If you’re packing a lunch for your little one, don’t just think about what goes into the bag. Think about how to keep it cold. That’s the message from a new study by nutrition scientists at the University of Texas at Austin.

Looking at more than 700 lunches packed by parents for children at nine Texas preschools, they found more than 90 percent – even with multiple ice packs – reached unsafe temperatures. Cold foods should be kept below 40 degrees Fahrenheit, while hot foods need to be above 140 degrees. These lunches were between 40 and 140 degrees, the “danger zone.”

A large range of bacteria can grow in food in the danger zone, “too many for me to list,” says study author Fawaz Almansour, a graduate student in the university’s department of nutritional sciences. The best known food borne illness is probably E. coli, and preschoolers are four times more susceptible to infection than adults, Almansour explains.

His study, the first to look at the temperatures of preschoolers’ sack lunches, was published online Aug. 8 and in the September issue of Pediatrics. Almansour says the results were a surprise, as he knew many parents were using ice packs. “We didn’t know the temperatures were bad when we went in,” he says. “I was shocked. More than 90%. That’s really high.”

The study didn’t look at rates of illness due to unsafely stored lunches, but Almansour says parents could be assuming their child’s food borne illness is just a virus they’ve picked up at preschool. “No one would even look at the food as the culprit.”

Here are his recommendations for keeping your preschooler’s lunch in the safe zone:

1. Keep your child’s food refrigerated until you are ready to leave the house in the morning. “Don’t leave your food out on the counter in the morning,” says Almansour.

2. Place the food into the smallest insulated container that will hold it, along with multiple ice packs. He saw many parents in the study placing their child’s food in oversize containers. “The ice packs have a hard time cooling that.”

3. As soon as your child arrives at the childcare center, someone should take the food out of that insulated container and place it in a well-maintained, working refrigerator. The few centers with refrigerators in the study tended to leave the food in the containers, but this keeps the refrigerated air out of the lunch, and keeps it from cooling the food. Researchers also found refrigerators that were poorly maintained, or even left open.

“If the childcare center does not have a refrigerator, ask for one,” Almansour advises. You might need to get in there and do some fundraising among fellow parents, but he insists it is worth the effort. “Ice packs were not enough,” says Almansour. “Ice packs are not the solution for these lunches.”