There have been quite a few stories in the news of children and pets being left in hot cars (some resulting in death). Some people do this on purpose thinking "I'll just be a minute and the windows are cracked," (usually with pets) but majority of the time, when a child is involved, it is an accident.
This video is an eye-opening visual to how it can happen. It is very rarely neglectful parents that leave their children in the car. It can be something as simple as a change in routine or sleep deprivation that can cause our brains to go into autopilot.
If you are afraid of accidentally leaving your child in the car, you can leave a visual trigger for yourself in the front seat (teddy bear, diaper bag, etc.) or put your purse or cellphone in the back seat with your child so you have more than one visual trigger for your brain. For more information you can go to http://www.kidsandcars.org/
Good parents make mistakes, don't be too quick to judge a person as "neglectful".