I don't agree with smacking the child, BUT it is very frustrating watching children make a mess of your shop. I had a kid throw a can of red bull on the floor the other day, laugh, and his Mum goes 'just leave it' and pulled him on to carry on shopping. I heard it from the next aisle and went to see what happened, but she made no effort to tell anyone her son had spilt a can of drink (accidentally or not), so there was a massive wet patch in the middle of the floor which is a danger to customers and staff.
Kids regularly break glass jars because they wander off and Mum or Dad isn't watching them/has lost sight of them. They will take items from the bakery, half eat them and drop them around the shop therefore not paying for them either. Other times they faff around with the chiller doors and have broken them on occasion. I will and do ask children to let go of the doors or if they could please not run around the shop etc, but the looks I get from some parents if I dare utter a word
I don't think smacking is right, but I wouldn't have left the store immediately, I would kick up a fuss there and then. Accidents do happen in shops but it is frustrating working in retail. We had a 3 YO run into the glass door at my work and the parent had a right go. Its not our fault their child ran into a door which has a big 4 foot sticker on it 6 inches up from the ground. It was an accident.
Swings and roundabouts with perceptions, I'm not sure how clear cut this story is. I still don't think smacking is acceptable, I don't think touching anyone else's child in that situation is acceptable unless its to remove them from danger. But it is very frustrating working in retail if you have a few children with parents who aren't good at keeping their eye on them, or don't care.