In the years since, such tragedies have increased more than tenfold -- leaving advocates pressing for new safety measures such as child presence alarms.
"Why isn't the auto industry involved in helping to solve this?" asked Janette Fennell, president of the nonprofit advocacy group Kids and Cars. "Why isn't the national Highway Traffic Safety Administration doing anything to help protect the children? This is something that's very solvable, it's predictable and it's also preventable."
From 1990 to 1992, before airbags became popular, 11 children died of hyperthermia after being left in cars, according to a study by San Francisco State meteorologist Jan Null.
In 2003 and 2005, when parents had learned to buckle children in the back seat, the number of deaths spiked to 119.
For years, the basic technology has existed for reminder alarms to alert a driver leaving a vehicle that a child remains in the back seat.
One mechanism, announced in a 2002 news release, was developed at NASA's Langley Research Center, spinning off aircraft-testing technology.
It combines a car seat presence sensor with a key chain fob that beeps when the driver moves too far from the vehicle.
"It's not a very complicated device," said NASA spokesman Chris Rink. "There's a pressure switch, a plate underneath their bottom, that sets the alarm. The only time the alarm is turned off is when you remove your child from the seat.
But five years after its invention, the Child Presence Sensor alarm has yet to hit the market.
NASA is in the final stages of licensing the patent to a manufacturer, Rink said.
"Sometimes it just takes a long time," he said. "Larger companies may not be interested for whatever reason, and some of the smaller companies may not meet our qualifications to manufacture and eventually market it."
A similar product, the ChildMinder, links a "smart" chest clip to a keychain alarm. Orders are being taken online at http://www.babyalert.info.
Terrill Struttmann, founder of the Missouri-based advocacy group Kids In Cars, said people periodically contact him about child-reminder alarms they've invented.
"The problem they run into is marketing this product," he said. "If a parent is in a Babies R Us and sees it, it's going to be that false sense of security: 'I would never forget my child.'"
In the past five years, at least 199 children have died of hyperthermia after being left in cars, said Struttmann, who maintains a database of deaths from various causes of children left in cars.
The stories are eerily similar: The victims tend to be infants younger than 2 who are likely to be lulled to sleep by the ride and may be in rear-facing seats, Struttmann said.
In most cases, the accident was preceded by a change in schedule, with mom or dad dropping off the child when the other parent normally does.
"I've personally spoken to a couple of the parents that this has happened to ... and from my experience it's been very lovely, very caring parents who simply forgot about their child," Struttmann said.
The tendency to blame parents, Fennell said, has impaired the larger discussion of how to solve the problem.
"Probably the biggest problem is nobody thinks it can happen to them, and unfortunately it continues and continues and continues to happen," she said.
To understand, all parents need to do is remember their closest call: the moment of panic when they realized their own mistake could have seriously harmed or injured their child.
"We all have a story like that," Fennell said.
"These are the cases where you don't get the grace of God. These are the ones that go bad."
Long-term solutions will require more than public education, Fennell says.
"If you leave the keys in the car, you get a warning. If the headlights are on, you get a warning. If you don't have the seat belt on, you get a warning."
Child presence alarms should be built into new cars and car seats and should be readily available for purchase by parents, Fennell said.
"It's absolutely ludicrous that it hasn't been brought to market," said Fennell. "The technology is there to save lives.
"We can prevent this. This does not have to happen."
Reach Sara Steffens at 925-943-8048 or firstname.lastname@example.org.