(CBSMIAMI.COM) — Is your kid’s brown-bagged school lunch unsafe? A new study suggests sacked lunches are breeding grounds for bacteria that cause vomiting, diarrhea, or even death in some children.

A new study in the September issue of Pediatrics found parents may be unwittingly packing a breeding ground for bacteria due to high temperatures.

For the study, researchers examined 705 sack lunches at Texas child care centers 90 minutes before lunch time. Even though nearly half of them contained one ice pack, only 1.6 percent of the lunches were kept at what researchers considered a “safe temperature zone.” That translates to 98-percent were at unsafe temperatures, even with ice packs.

Doctors say the findings are of particular concern for younger children.

“In a daycare age group, kids under 4, are about 4 times more likely to get serious illnesses from food poisoning than somebody’s whose older and so this is an age group that we’re particularly focused on,” said pediatrician Matthew Weissman.

The study showed that more than 97 percent of meats, 99 percent of dairy items, and 99 percent of vegetables were stored at unsafe temperatures and only 22 out of the almost 1,400 food items were considered safe.

What should parents do? The USDA’s Food Safety and Inspection Service recommends that parents freeze some types of food, like mayonnaise-less sandwiches, the night before to keep them cool until lunch time. Lunch bags should be well-insulated and contain an ice pack or a frozen juice box to cool down the bag’s contents.

Doctors acknowledge most kids don’t get sick from packed lunches, but say it’s about reducing the risk of food-borne illness.

Experts say at school, be sure lunches get into a refrigerator. Use fruits with peels, like bananas and oranges, and foods not so temperature dependent, like peanut butter. Also, talk with school administrators about your concerns.