A woman I know has 4 kids under 4, which includes a set of twins. Today she was trying to decide how to go to the post office with so many kids. She asked on facebook if we thought it was okay for her to leave the kids in the car, and run in to the lobby for a couple of minutes. There are glass doors, and she would be able to see her car from there. Personally, I don't think it's any more dangerous than going to the bathroom with your kids unattended, but I told her that I would just worry that someone would report her. (By the way, I offered to go with her, but she didn't accept.)
That reminded me of a story a friend told my husband. He said that one day he took his boys with him to the grocery store. When it was time to go home, and he was putting the groceries in the trunk, his kids begged him to let them ride home in the trunk of the car. At first he resisted, but then he started thinking that they lived not far away, and the kids would only be in there for a few minutes. He finally gave in and told the kids that just this one time they could ride in the trunk. They were SO excited!
He didn't think too much more about this incident until CPS showed up at their door. Someone had seen him put his kids in the trunk and called CPS. Their family had to go through about 6 months of probation and had to make themselves available for inspection at a moment's notice.
I know that we have laws for a reason, and that there are many parents that need close governmental supervision. But some days I long for the days when kids could be kids, and parents were free to use their best judgment.