This was in a liquor store rather than a supermarket. I had stopped in for a bottle of wine to give to the hosts of a party. While I was selecting an appropriate bottle, my daughter (who had just turned four) picked up an especially pretty bottle of vodka, covered in little square blue mirrors. Blue is her favorite color. She danced around holding the bottle until I was done making my purchase.
I left the cashier and told her, "It's time to go—you can p455ut that back on the shelf now."
She replied, in a happy, chirpy voice loud enough for the whole store to hear, "But I love vodka!"
I'm cheating a bit here because it wasn't my kid and it was in a bank rather than a supermarket, but it's along the lines of the question.
About 22 years ago my sister was standing in line at the bank with my beautiful niece who was about 3 or 4 at the time. Little Emily was standing in front of my sister and in front of Emily was a man. All of a sudden Emily announced in that loud way little kids do, "mummy, that man's bottom just burped". My sister was mortified and began attempting to shut her child up, the man immediately left the queue as something terribly important had obviously just come to mind and the bank remained quiet as my niece argued the veracity of her statement. We still laugh about that to this day and prefer bottom burp to fart.