This all seems so strange to me.
When I was a kid in the late 70s and early 80s, I must have spent hundreds of hours in the car waiting for one or both of my parents in stores.
I hated stores and was not well-behaved, so it was a good place for me to wait.
By the way, this was not unusual. It was very, very, very common to have kids wait in cars, even in Florida where I grew up.
This is one small part of the social changes that I discuss from time to time on this site that many people seem intent on denying but that are common and numerous.
My parents dragged both of our ill behaved asses into stores. I think it was partially because when we were both preschool age, my brother managed to start the car & put in reverse/neutral twice. (To quell my brother’s tantrums, she’d let him turn the key in the ignition before we drove off. He loved cars.) I don’t really remember being left in the car before the age of 8, and certainly never with the car running.
Would they leave you with your little sister? I was primarily concerned with self amusement (I’d carry a book to read when my parents drove to read until I felt nauseous) and was just as likely to fight with him as ignore him.
Most states don’t have laws about children in cars even now