Unfortunate, but you just have to make children understand that even if grown ups say these things sometimes, children must not.
I must have been 11 and new to senior school,when I heard a girl saying 'Balls!' (mild now, I know,). With no clue that it meant anything other than round things used in games, I came out with it at the family dinner table.
After looking askance, my father's merely told me that it was not a word for me to use, 'particularly not in mixed company.' !
It was quite a while before I found out why not!
When we lived abroad our very small dd took a school bus from our compound to school, with a lot of older children who evidently didn't moderate their language.
At still only 4, on a visit to the UK, and in front of some very 'proper' relatives - not elderly maiden aunts but those of our age who had young children of their own, she came out with the F word!
Talk about the temperature plummeting to sub zero - they were so appalled, and our explanation that she must have picked it up on the school bus cut little ice - I swear our names were mud for a long time.
After having it explained that it was a very rude word and she must never say it again, she never did - at least not that I ever heard.
But the relatives' reaction always struck me as seriously OTT - they couldn't even begin to shrug it off once we'd explained, let alone laugh about it afterwards.