The thing is, something could happen to you while you're away. The few minutes in the car won't hurt the child, but if something happens to you, the child is still there. And if you locked the car, the child can't get out.

I'm all for letting kids play with little or no supervision. (Depending on the surroundings, of course; a place near my home where kids can build huts has the explicit rule that kids under 8 need adult supervision at all times, which makes total sense. A mother was upset that someone confiscated the hammer and saw her kids were using while she was away. That mother was wrong.)

But what's important is that if you trust your child to take care of itself, you give it the means to do so. Locking a kid in a car is not that. I'd rather let it play in the parking lot or a field next to it.

So I think the decision to leave the kid in the car is still a bad one. And not even just because of the danger, but because of teaching it about choice and consequences: The kid wanted to come along to the shop? Then it's coming inside. The kid thinks a game is more important than new earphones? Then it's not getting new earphones. Teach the kid consequences.