That is the biggest bug bear of mine regarding supermarket parking. There is nothing worse than struggling with a pram, a baby and your shopping bags in a proper customer parking space. I hope when the time comes for you to have kids Sam that someone parks there car in the parent and child bay and then watches you struggle further up the car park. Even now although my son is nearly 6 it still annoys me watching people who obviously don't have a child park here. I have not used the parent and child bays since my son started walking as I feel that people with babies and toddlers need is greater.
On the subject of car doors, a local child (aged about ran a stone down the whole side of my car a few weeks ago. I hear she's moving to Perth!!!