Leaving child in car while Mom shops?

Nicole
Just curious how common this is? I witnessed 2 children in their car seats while the mom shopped inside a store for 30 minutes. Yes her car was parked outside with the windows cracked. That was her excuse for why this was acceptable. 
I called the police to handle the situation as I didn't think it was wise for me to confront her being 9 months pregnant.
Just curious if anyone else thinks it's okay to leave their kids in the car. Is this common?