As a teenager I had a Saturday job in Primark. One day I came out of the staff lift into the loading type area, where no customers were allowed, and found a woman letting her approximately 4 year old grandson wee in a metal container. It looked a bit like a bin in that it had a slot near the top but had no bottom on, so the wee was seeping underneath straightaway.
I was quite dumbfounded and think I asked what she was doing and she huffed a bit and said something like 'well you've got no toilets and he was desperate!' I said we would have let him use the staff toilets if she'd asked, as we tended to take people there if a child needed to go.
She dashed off quickly and I was just deciding on how best to clean up when a manager came in. She was outraged and tried to find the woman to make her clean it up herself but the woman must have legged it out of the shop as she was nowhere to be seen.
On a side note, when my daughter was potty training I did use to take a potty out with us but that was because she didn't like sitting on big toilets - but I always made her use the potty in a toilet cubicle, not just anywhere in public!