I... don't understand. Are their children coming with them for the entire grocery shopping experience, and then just being left completely alone while the parent returns the cart? Could they not just bring the child with them to the cart return?
I think most parents get their kids in the car first because kids hanging around in the parking lot with cars pulling in and out is hazardous and kids can be dumb. Hard to keep an eye on them while you're unloading things so you put them in first. Then of course if it's warm out the car is hot and kids will be complaining so the parent starts the car to get the AC going while they secure the kids and then unload the groceries. Once done of course they have to decide... walk away from the running car with your kids inside and put the cart away, or not. I can understand why sometimes they dont.
Lol back when I was a kid, my mom would wait in the car with the AC while I returned the cart.
Though unless I'm misremembering, I think I often volunteered for cart return duty as it would give me a chance to push the cart super fast and ride it.
How far away are these cart returns? Its not taking more than a minute. If you're afraid of the kids getting kidnapped, lock the door. They won't melt even in the Texas heat where I had them.
If parents are doing it for this reason, it is just a justification to be lazy.
Have kids. Always have returned my cart even when shopping with them. If it takes you longer to return the cart than it would for some person to find your child and get them out of the car seat by the time you got back...well, that's on you.