. . .Children that small should NEVER be left unattended in a vehicle under any circumstances, especially if it is running . . .
It's illegal here. But every summer another kid gets hurt in a car.
Parenting is like motorcycling. It doesn't matter who has the right of way. On a motorcycle you'll stop or seriously regret it.
It doesn't matter if a parent takes every logical and illogical precaution. If your kid gets hurt, it's on you, forever.