I'm the parent of two toddlers and I can see how it happens. It's not quite as serious as leaving them in a hot car, but I've been in a rush and so distracted by work or life that I've put them in the car and driven away without remembering to fully buckle them into their carseats.

Realizing that you've potentially endangered them is an awful feeling, and a stark reminder to slow down and remember what's important in life.

Luckily they've gotten precocious enough to yell at me "Daddy I'm not buckled" so it doesn't happen any more.