I have a mom who leaves the baby in the car (older sibling comes to me) and it's sometimes quite long IMO. I'm not sure if the car is running or locked however as I feel it's her decision. It's not what I would do though. Another mom (and grandparents as they do pick up and drop offs a lot too) always bring the 6 yo big brother in. I guess it's just what they feel comfortable with?

Your situation sounds quite dangerous though!! I'm really not sure what I'd do however. Helping undress or have ready for pick up maybe? Encourage mom to bring child in?