A mother lets her children - aged just nine and six - swear all the time at home because she insists "language shouldn't be censored".
Lucinda Hart, 47, even allows Rafi and her younger sister Aelfrida to tell her to "f*** off" in private.
The author, who is from Mullion, Cornwall, insists the language is "natural" and should be used in preference to euphemisms.
Lucinda said: "I do not censor words with my children. That is not what language is for.
"I love language - it's natural to swear.
"I tell them they can say what they want at home. They know the invisible boundaries."
But the mother doesn't allow her daughters to swear in public, and tells them they must never make personal comments to people.
Lucinda, whose children were born via IVF, has taught her daughters about anatomy from a young age - using their correct terms instead of words such as "tinkle" and "minnie".
"They know the invisible boundaries," Lucinda said.
"The girls might say, 'F*** off, mum'. But the dinner ladies always say they are smiley and kind.
"I tell them to never make personal comments to people.
"I'm not going to make up words. Anatomy is beautiful.
"They know about a vagina and penis. They knew about egg and sperm from a young age.
"And I say to the girls, 'Don't say poo say, s*** or c***.
"A person at work would always say, 'Oh sugar' instead of swearing. I just think say it or don't say it at all."
Lucinda talks to her daughters about language to help them become at ease with it.
She said: "I had a conversation with Rafi about the word 'f***' and how it originated.
"She is an amazing writer. She's already at ease with language."
She said the girls know the "boundaries" and don't swear at school or in front of other mums.
Lucinda said: "They never say it out at school.
"If either the girls did swear at school and the school called me in I would say, 'Sorry - it spilled over from home'.
"To me it's not a big deal [swearing]. It's like an extra bit of punctuation."
Lucinda is encouraging other parents to not censor their language and not worry about holding their tongue.
She said: "What matters is your kids are kind and well-behaved.
"There are so many things to worry about as a parent - don't worry about things that don't matter.
"Language has been changed and wrecked in so many ways but these old words are pretty much the same.
"I like the idea that people hundreds of years ago would say the same thing when they stub a toe or whatever.
"These are words that have endured."
