No excuse for leaving a child in car.

It happened again this week: Another grown-up left a baby alone in a hot car.

For those who never lost a toddler in Wal-Mart, backed over one in the driveway or found one at the bottom of a pool, it’s hard to understand how children end up dead in the backseat of the family car. There are only three ways: The adult in charge forgot the baby, the adult deliberately left the child or nobody was supervising when the toddler crawled into an unattended car.

Now, legislation introduced in Congress seeks to require car manufacturers to install a “back seat reminder” to notify parents and caregivers so they don’t forget Junior is in the rear seat and obliviously toddle off into the grocery store without the tyke.

Would such a device be a valuable lifesaver for helpless babies? Or is this another case of government trying to legislate safety where common sense would do? You decide.

Unbelievably, 17 percent of 739 children who died in hot cars over the last 19 years — that’s 120 tiny souls — were left there on purpose by the adult watching them. The grownup’s explanation is always a variant of “I’ll only be gone a minute.” Really, that excuse is worn out.

Yet, it’s what happened again Monday when a hotel housekeeper left a 2-year-old child in a car seat in the parking lot of Disney’s Grand Floridian Resort & Spa. The toddler’s mother was in labor, and Myriam Lubincadet, 37, ran in “for five minutes” to ask for the afternoon off to babysit.

Forty-five minutes later, the temperature in the child safety seat was 113.5 degrees while the temperature outside the car, with windows partly open, was 93 degrees.

Forget the heat. Who leaves a toddler alone in a car for 45 minutes in the parking lot of a big tourist resort where anyone could snatch her? They might as well have pinned a sign on that baby: “Free. Take her.”

Folks, there is no fixing stupid. You are either aware of the snares of the world around you or you’re not. Neither audible nor visual reminders will prompt this 17 percent of idiots to take their children with them. Sadly, this apparently still needs repeated: Do not leave toddlers in cars alone. Ever. Not for a nanosecond. Not if they’re sleeping. Not with older children. No. Just no.

Lubincadet, protesting that she loves the child who is her cousin’s daughter, was arrested on a charge of child neglect. Thankfully, the toddler wasn’t seriously hurt.

Besides the children left deliberately, there are another 198 dead children, or 28 percent, who perished of heat stroke when they climbed into an unattended car and couldn’t get out. These are parents and caregivers who simply aren’t watching their kids for whatever reason. Who doesn’t check on a 2-year-old they haven’t heard for two minutes?

Together, those two reasons for hot-car deaths account for 45

percent of the children lost since 1998, according to noheatstroke.com, a website dedicated to tracking and preventing deaths.

Now, we come to the toughest reason, the 54 percent of dead children, or 376 fatalities, whose caregivers forgot the little ones were there and efficiently rolled up the windows, locked the car and left.

What heartbreak to learn that a child died in a horrific way while you were distracted or focused on something else. In the case of Myles Hill, the 3-year-old Orlando boy who didn’t survive 11 hours locked in a daycare van, the driver got distracted by a telephone call and simply failed to count heads when the van emptied. The fallback was that someone was required to see Myles, then check him in. He was checked, but no one had seen him.

The driver, Deborah Denise St. Charles, 51, was distraught when she learned what happened. She’s been charged with aggravated manslaughter.

Already, General Motors has a rear-seat reminder on more than 20 models of GMC, Chevrolet, Buick and Cadillac vehicles. This summer, Nissan introduced its own version, which honks at a driver who opens the rear door before a trip but leaves the car without opening it again.

In 2015, car seat maker Evenflo came out with a chest clip sensor that tells the driver if the harness is still engaged when the car is turned off; Waze, a smartphone app for maps and traffic, will remind the driver to look in the back seat.

Has it really come to this? Is this society so obsessed by daily drama that we can’t remember a

baby? So far, 39 children died in hot vehicles across the nation this year — six of them in Florida. That’s shameful.

Prediction: If Congress mandates a rear-seat sensor, a lot of folks who say they forgot will suddenly have a new story: “malfunctioning” sensors.