Oh gosh I have a few!
The first my daughter aged about 3/4 when out shopping, sat down and shouted, "I'm nit going into Marls & Spensives again!! Obviously it has always since been called that!
The 2nd, my schoolfriend was a primary teacher, in a not great area of Rotherham - she overheard some children in the play house say "let's play mummies and daddies; I'll be the dad, am working nights and going to rob some houses"!
The 3rd, young lad belonging to friends - playing I Spy in the car. "I Spy something beginning with J". The 4 adults just could not get it, an eventually gave in. "Jewel Carriageway, you lot are stupid!"
Same lad, his parents had some odd friends. Parents evening, his teacher told them that he had a remarkable imagination ... oh why they asked. He had written a very interesting story about his 'Uncles' coming for the weekend. They had a hearse, and they'd driven about in the hearse with a plastic skellington in the back. It was all true!
One day his dad took him to a football match for the first tine, and he had obviously been hearing much f'ing and blinding. One day some weeks later, his mum took him to a local cafe where she was well known. He asked to go to the loo at the other end of the cafe, and she told him to go. A few minutes later, the door opened and he shouted "mum, there's no f'ing toilet paper"! She wanted the ground to open up and swallow her!