What they said. I’ve never forgotten my kid (or someone else’s - a good thing, since I’m a babysitter!), but I’ve come close. Big carseats are the thing these days, often “3-way” carseats which serve as rear facing for the littlest ones, but built big enough to seat a 100 pound kid. They’re built to enclose the child in plastic and fabric from three sides. Put it in facing the rear, add an infant who’s been up all night, a parent who’s also been up all night (with the baby, natch) and I can see where overtired parent+huge carseat +baby falls asleep would get spacey and make a horrible oversight. Toss a deviation from normal routine (like Mom is s’possed to take the baby to the sitter on her way to work, instead of Dad, who normally does it) and things can get understandably and still horrifically bad really quickly.
Here’s a picture of an infant in the rear-facing position in a medium sized car seat. Imagine how that looks from the driver’s seat, or even walking along the side of the car. The baby is practically invisible. *ETA: I’m sorry, that’s a **small **seat, designed for rear-facing use for infants under 20 pounds and a year old only. I can’t find a pic of a rear-facing 3way seat in use. *Other smaller seats have sunshades - great for when the carseat is doubling as a stroller seat, but again, blocking the view of the baby from a distracted, tired parent.
I also get upset because news stories about things like this make it very hard for me to leave my daughter for even a moment in the car alone. I’ve had strangers standing next to my car peering in at her when I got back from putting the cart in the corral at the grocery store - never out of sight of the car, but they didn’t know that. Just yesterday, she was sleeping in the car (and sweaty despite the air conditioning, 'cause she sweats when she sleeps regardless of the ambient temperature.) I wanted to grab a Monster at the convenience store. Knowing how bad it would look to a passerby, I wrote “In [name of store] buying beverage - left at 2:07, please don’t call the police unless I’m not back in two minutes,” on a piece of scrap paper and wedged it into the window weatherstripping. And the whole time I was still watching out the big window (and I chose the big window store instead of the drugstore across the street with energy drinks on sale for just that reason). I hate having to be that paranoid, but it’s better than having a perfectly understandable Good Samaritan call the cops on me because a sweaty unconscious baby was in a locked car for 58 seconds.
Who once forgot her kid was in a carseat on top of the car - but remembered before actually starting the car and driving off, thank goodness.