Christine Zone, a day care teacher in Strongsville, Ohio, sees some scary things in kids' lunches: food that's lovingly but improperly packed, and left to slowly warm up as the morning wears on. "I go crazy thinking of the multiplying bacteria!" she says. "Parents will microwave leftovers in the morning but then the container sits out until noon. They send string cheese and yogurt without ice pack. Their kids sip on the same bottle of water all week that's never been refrigerated. They're disasters waiting to happen!"

Zone's concern is well-founded. "Forty to 140 degrees F is the danger zone for food," says Elisa Zied, an American Dietetic Association spokesperson and registered dietitian in New York. In other words, perishable food needs to be kept at temperatures below 40 degrees F (5 degrees C). If it's reheated, it has to reach an internal temperature of 140 degrees F (60 degrees C) or more. Otherwise, harmful bacteria can multiply to dangerous levels, possibly making kids sick. "Children have developing immune systems, which means they're more susceptible to the ill effects of spoiled food," says Zied. "When your child gets sick, it could be a 24-hour bug, but it could also be food poisoning."

Here are five easy steps for keeping your child's lunch safe.

Make a good start. Wash your hands before and during food preparation, and always store food in clean containers. "Don't just dump the crumbs out of the container from the day before and put another sandwich in," says Zied. Use fresh food (leftovers, such as cold chicken, should be a maximum of four days old) and give produce like apples a scrub to remove dirt and pesticides. Keep portions small enough (for example, cut sandwiches in half or quarters) so that they stay evenly cool. Wipe out the lunch bag or box after each use with mild soap or a bit of baking soda and water. Get ideas for tasty lunch sandwiches.

Keep it cool. There are lots of cute and kid-friendly insulated lunch bags and boxes available, so have your child pick a favorite. Chill the food and the bag in the fridge overnight so you're ready to go in the morning. You can also use mini-ice packs, frozen juice boxes or water bottles to keep things cool. "One good tip is to fill a water bottle halfway, freeze it, top it up with water in the morning, and your child will have a nice cold drink at lunch," says Zied. (According to the Food and Drug Administration, freezing disposable water bottles is safe.)

Know what needs to be chilled. If a food item is normally kept in the refrigerator - such as string cheese, yogurt, mayo, lunch meat, milk or leftover pizza - it needs an ice pack in the lunch bag. (Fruit and veggies are fine at room temperature for a few hours.) Refilling the same water bottle over and over again without proper washing or refrigeration is not a good idea, either. A study conducted at a grade school in Calgary, Alberta, found that many of the kids' water bottles contained fecal coliform and other nasty bacteria, in part because they weren't washed and dried between uses.

Skip the hot stuff. "Sending soup or chili in a thermos, or food that has to be reheated in the microwave, is generally not worth the trouble," notes Zied. "You're not going to send your child to school with a thermometer to make sure the temperature is 140 degrees F or more!"

Wash little hands. Encourage your child to wash her hands before she eats her snack or lunch. Zied suggests tucking an individually packaged hand wipe into her lunch bag. Get hand washing tips for kids.