I’m not a parent, but while in college, I was a regular babysitter/mother’s helper for a family with 3 kids who were 1, 4, and 7 at the time. I drove them around a lot on errands. Never, ever would I have thought of leaving them in the car while I ran into a store to get something.
If you are a babysitter, that is somewhat different. Where you are also makes a big difference. I live in a very small town, with small parking lots, small lines, and most of the people know each other.
My question about leaving them alone in the driveway stands. If the four year old is asleep, did you ever haul in the one year old first, leaving the four year old momentarily unattended?
You’re not a parent.
So you have no clue.