What are children to think when their mother’s nose suddenly gets smaller, her breasts bigger, or her belly flatter? How should parents explain the changes?

Some prefer fantasy — “it was a mysterious gift from Santa Claus” — or lies — “Mommy needed a smaller nose in order to breathe better, Honey.”

But Dr. Michael Alexander Salzhauer, a plastic surgeon from Florida, is a fan of honesty. He has written a children’s book, My Beautiful Mommy, that bluntly explains it all.

“You can deny it or … face the issue head-on,” he tells Madeleine Brand of his 21-page illustrated story of a mom who gets a tummy tuck and a nose job.

His tale is narrated by a red-haired girl, about as tall as her mother’s tiny waist is high. On the way to visit a doctor with the build of a superhero, Mommy tells the girl, “My nose may look a little different after the operation.”

“Why are you going to look different?” the girl asks.

“Not just different, my dear — prettier!” Mommy responds.

Salzhauer says he agonized over that bit of verbage.

“I could have said ‘straighter,’ but I figured an astute 7-year-old child or 6-year-old child would say, ‘Why do you need your nose straighter?’ And that would inevitably lead to the question of ‘prettier.’ ”

Salzhauer, who had a nose job himself when one of his daughters was just 4, says he saw a need for such a book in his own practice. Many of his female patients bring their children to post-operative visits, causing confusion for the youngsters.

“They typically associate a visit to the doctor’s office with sickness and death — and when you don’t give them information, they fill in the gaps with their imagination,” he says.

He also wants to help children understand why their mothers are covered in bandages and unable to move much after the procedure.

“These operations are not simple surgery in the morning and lunch with the girls at noon,” he explains. “These operations require a lot of down time — two or three weeks, typically — and they turn your household upside-down.”

The book shows how everyone can aid Mommy’s recovery after the operation. Daddy makes breakfast and takes the little girl to school. Brother Billy “even picked up his clothes and put them in the hamper without being told.”

Salzhauer emphasizes that his book is meant specifically for patients who have already decided they are going to have a tummy tuck or rhinoplasty.

“It wasn’t meant to be read as a children’s bedtime tale like Goodnight Moon,” he says.

Still, mothers at a park in Santa Monica took issue with the message.

“I would not read this book to my young child,” said Deirdre Nagel, who has an 8-month-old daughter. “I just get concerned that if you’re reading this book to a young child … it sends this message that this is what all women should look like.”