According to the following article parent packed school lunches reach temperatures during the day that make them unsafe to eat. The article is not very long so I am posting it in its entirety so you need not go to the link.
Children's packed lunches too warm to be safe: study
Aug 9 (Reuters Life!) - Tests of more than 700 preschoolers' packed lunches found that fewer than 2 percent of the meats, vegetables and dairy products were cool enough to be safe, according to a U.S. study.
One in six U.S. residents gets food poisoning every year, according to the U.S. Centers for Disease Control and Prevention (CDC), but it is unclear how many cases are caused by lukewarm sack lunches.
The study by Fawaz Almansour, a doctoral student at the University of Texas in Austin, was the first to check how the food that children take to school is doing in terms of health about ninety minutes before they eat it.
"It was a shock when we discovered that more than 90 percent of the perishable items in these packed lunches were kept at unsafe temperatures," Almansour said.
According to his study, published in Pediatrics, some 705 lunches packed by parents for children in full-time daycare centers were checked for the temperature of perishable food items and the number of ice packs included.
The CDC says that perishable foods kept between 4 to 60 degrees Celsius (40 and 140 degrees Fahrenheit) for more than two hours are no longer safe to eat.
Some 39 percent of the lunches had no ice packs, while 45 percent had at least one. Some 12 percent were kept in refrigerators.
Still, 88.2 percent of lunches were at ambient temperatures.
"Even with multiple ice packs, the majority of lunch items were at unsafe temperatures," Almansour and colleagues wrote.
Almansour said the study had been an "eye-opener."
"It shows there is a problem," he added, recommending that lunches be packed with lots of ice packs and refrigerated once the children arrive at school.
Children's packed lunches too warm to be safe: study | Reuters (external - login to view)
Having read the article I am wondering if this is not another case of over reacting to a practice that has been going on for decades. After all during the era that I attended school (the 1950s and 60s) refrigeration of a school lunch simply did not happen. No one worried about the danger of the school lunches packed by our mothers and yet I do not remember any cases of food poisoning. Of course, perhaps we were poisoned and simply thought that we had a case of the flu or some other stomach disorder.