THURSDAY, Sept. 12 (HealthDay News) -- Schoolchildren should start each day with a clean lunch bag or box to help prevent the growth of potentially harmful bacteria, according to a food safety expert.

Insulated, vinyl lunch bags are most effective in keeping foods cool and fresh during the day, and when kids get home from school, parents or caregivers should clean the bags with warm soapy water, and allow them to dry completely overnight, said Rutgers University professor Don Schaffner, an extension specialist in food science.

This is just one way to ensure children's school lunches are safe enough to eat, noted Schaffner, who is also a spokesperson for the Institute of Food Technologists.

"When you're packing a school lunch, it's important to think about the perishability of the foods you're making," Schaffner said in an institute news release. "Perishable foods can remain at room temperature for no more than two hours -- one in the summer due to the heat. Properly refrigerated foods can last a long time, but most schoolchildren won't have access to a refrigerator where they can store their lunchbox."

Parents and caregivers can take other steps to make sure children's school lunches are safe, including the following:

• Consider packaging. Use sealable, disposable sandwich bags or dishwasher-safe reusable plastic to ensure a child's lunch is packed in a clean container.
• Opt for nonperishable items. If possible, pack foods that do not need to be refrigerated, such as single-serve fruit in prepackaged containers. Peanut butter and jelly sandwiches are another good option. "It's a kid favorite and neither ingredient is quickly perishable," Schaffner pointed out. "You don't have to worry about refrigerating it, and it will last from the time you prepare it in the morning until kids consume it at lunchtime."
• Pack ingredients separately. Older students may be able to assemble their own lunches at school. Packing bread in one container and placing meats and cheese in a separate container with a cold pack can help keep food fresh.
• Keep it cold. Cold packs can keep cold food cool, but can't sufficiently cool down food that is room temperature. To ensure that perishable food stays cold enough, make lunch the night before and keep it in the refrigerator. In the morning, pack it in a lunch box with a cold pack so it stays cool. Cold packs should also be placed directly next to any perishable foods, such as yogurt or meat. They should also be washed after every use.
• Keep it hot. Hot foods, like soup or stew, should be stored in an insulated container. Before placing the hot food in the container, fill it with boiling water and let it stand for a few minutes. Then empty the container, add the hot food and be sure to seal it firmly.

"Not planning adequately, not thinking about the amount of time it's going to take, from the time that food is prepared until that food is eaten, is a common mistake," Schaffner said. "At night, wash the cold pack and make sure it goes back in the freezer so it's ready for the next day. Give yourself plenty of time in the morning to wash your hands thoroughly before handling food. And keep stressing to kids the importance of washing their own hands before they sit down to lunch each day."

More information

The U.S. Centers for Disease Control and Prevention has more about food safety.