I don't know what its like where you guys live, but we have trolley bays in the carpark, a few of them, and inside the shops aswell. If I have both kids, especialy when my youngest was a baby I park near a bay so I can put them in the car and put the trolley back easily. Otherwise I pop them back in the trolley and back inside, then walk back.
But I don't see how people leave their trolleys wherever, you'd have to walk them back to somewhere so they're out of the way of a carpark surely?
Maybe thats why it's good we have to put money in, you'd make more of an effort I think.
Stray trolleys drive me insane! The poor guys who have to collect them all