This summer brings a push for new technology to stop those tragedies, CBS News' Jeff Pegues reports.
Even if it's 80 degrees outside and the car is parked in the shade, safety advocates say a baby can die in the backseat in as little as 10 minutes.
Now, there's new technology, some of it for phones, that may help prevent that from happening.
Precious Cargo is one of several startup technologies that can alert parents when their children are left behind. The 99-cent smartphone app pairs with Bluetooth to message the user when a child is onboard when their car stops.
Kimberly Johnston, the app's developer and mother of three, said even if the driver is in the middle of a telephone conversation, they will be reminded.
"If you're talking on the phone - that's one of the number one distractions of parents - it comes through your earpiece, so you hear it while you're on your conversation," Johnston said. "If your phone's on silent, it still comes on."
Two other alert systems, Babeep and The Hot Seat, are in prototype phase.
So far this year, 19 children have died from heatstroke in cars. In June, Justin Ross Harris was arrested and charged with murder in Georgia for leaving his son Cooper in the back seat of his SUV while he went to work.
On July 7, Lindsey Seitz's 15-month-old son Benjamin died in the back of her husband's car. Kyle Seitz was supposed to drop the little boy at daycare but instead drove straight to work. Benjamin sat in a car seat for several hours on an 80-degree day.
"You never think it can happen to you and then you wake up and have a normal day and then you find out in the afternoon that your son's gone," Lindsey Seitz said. "This can happen to anybody."
Public service announcements are designed to educate parents about heatstroke, a leading cause of non-crash vehicle-related deaths for children under 14. Most occur in overheated cars.
"Public service announcements are helpful, but we've been working on this for many, many years, and the truth of the matter is it's a very, very misunderstood situation," said Janette Fennell, president of the child advocacy group Kids And Cars.
"Nobody wakes up in the morning and says, 'I think I'll leave my child alone in the car.'"
Earlier this month, Kids and Cars asked the Department of Transportation for funding to research and develop technology which can detect when a child is left alone.
"You can't buy a car today unless it has a feature that turns your headlights off for you," Fennel said. "So who's decided it's more important not to have a dead car battery than a dead baby?"