I've done it, but it depends on where.  If the vehicle is 20' away and in view the whole time - or are you in the back of the store for 10 minutes waiting at the register?

Funny story - went to the grocery with the wife and two small boys in the van - they were probably about 3 and 5 - wife went to run into the store for a few things and got one car away and saw someone she new and started chatting.  I waited a while, decided to go into the store myself, told wife as I walked by - there was one car between her and the van and it was in full view - maybe 12 feet away. I heard the announcement over the intercom while in the store for the owner of the red Honda Odyssey to come to the front desk and figured out what was going down - a woman was standing there talking to the store manager obviously very agitated - I decided to get some entertainment and watched as the manager and irate woman stormed out to the parking lot, my wife - still 12 feet away from our boys and chatting had no idea what was going on when the two beelined for our van and tried to get in to the vehicle to rescue our 'abandoned' children.

My wife didn't think it was very funny when I strolled past them in the parking lot as she was in an argument with the two do-gooders haha.

It gets a lot easier as the kids get older - bottom line you should probably just do whatever it is your wife thinks is appropriate and your life will be much simpler.