WASHINGTON

IT’S a well-known fact that many esteemed children’s book authors don’t actually like children. The writer Judith Viorst isn’t exactly in that camp: She loves children, especially the ones in her own family. It’s just that they’re messy. And unpredictable. They wake up early and throw her writing routine out of whack. They demand attention she is sometimes loath to offer. They get chocolate on her favorite maroon velvet chair and dribble their drinks all over the floor.

Which is why she won’t allow Play-Doh, painting supplies or containers of glue inside her house, not even when her youngest son, Alexander, moved back in for a spell in the summer of 2006 with his wife, their three young children and a jumble of car seats, bicycles, sippy cups and children’s DVDs while their own house was being renovated.

“No matter how washable such materials claim to be, I don’t intend to check out those claims in my house,” she writes in her new book, “Alexander and the Wonderful, Marvelous, Excellent, Terrific Ninety Days,” (Free Press) a nonfiction diary for grown-ups that recounts the story of that tumultuous visit. “There are limits to any woman’s potential for further personal growth.”

This, after all, is a woman who sets the table for dinner parties several days in advance, and who said in September that she had already wrapped her Hanukkah presents. A woman whose combined linen and medicine cabinet is labeled with products for “cuts and bruises,” “colds and vitamins,” “shaving,” “hair,” “teeth,” “bowels,” “belly” and “beauty.” This is, after all, the author of a best-selling advice book called “Imperfect Control: Our Lifelong Struggles With Power and Surrender.”

“Nobody who knows me and loves me dearly would ever call me adaptable or flexible,” Mrs. Viorst said as she sat on the leafy front porch of her Victorian home on a sunny afternoon in late September. “I’m not.”

What Mrs. Viorst is, and has been for decades, is a keen anthropologist of family life. Her field work begins at home. “I was thinking of it as a growth experience,” Mrs. Viorst said of her son’s extended visit. “I thought it was going to be a very, very interesting collision between my super-organized, somewhat inflexible, inordinately plan-ahead self and my family values.”

Mrs. Viorst, a one-time garment district model, is a slim, elegant 76 with dark hair, a quick wit and a penchant for self-revelation. Since the ’60s, she has written dozens of children’s books, poetry collections and adult advice books, including “Necessary Losses” (1986) and “Grown-Up Marriage” (2004). But she may be best known for her children’s books about Alexander, starting with “Alexander and the Terrible, Horrible, No Good, Very Bad Day,” which has sold four million copies since it first appeared in 1972.

Her slight new volume — on “grandparenthood as a developmental phase,” as she puts it — mines deep veins: what makes a house a home, what happens when a control freak opens her door to toddlers and, more intriguing, what happens when the family she’s written about for decades squirms under Mom’s klieg lights.

TO step into the Viorst home is to defy a basic law of literature, to enter a strange twilight zone between fact and fiction. To anyone raised with the Alexander books, it’s incomprehensible that the mop-headed boy who went to sleep with gum in his mouth and woke up with gum in his hair sometime during the Nixon Administration could ever grow up, let alone become a father with children of his own.

So it comes as something of a surprise to see a photo — on a stairway with hundreds — of Alexander as an adult, with his wife, Marla, and their three children, all dressed up as “The Incredibles.”

By all accounts, not least his mother’s new book, Alexander has indeed grown up to be a fine man and a mensch. He works in community lending at a financial services firm in Washington, helping families in less fortunate neighborhoods buy their own houses. He competes in triathlons. He and Marla are the proud parents of Olivia, now 6; Isaac, 3; and Toby, 19 months.

At first, the Alexander Five, as Mrs. Viorst calls them in the book, considered renting their own place during the renovation. “I said, ‘You can’t do that, I’m writing a book about you,’” Mrs. Viorst recalled. This didn’t go over so smoothly. “There was a stunned silence,” she said. “All my friends laughed at me for being surprised.”

Over the years, in many books and a column she used to write for Redbook, Mrs. Viorst had always written about her family, and never asked permission. The last time she encountered significant resistance from her children, they were in elementary school, incensed that she’d written about their head lice for Redbook. “In one of the fanciest tap-dances of my life, I said: ‘Boys, you have made such a contribution to society. People who have been ashamed and horrified by this experience can now admit it.’”

Decades later, Alexander was taken aback to learn of his mother’s new project. “You’re writing a book about us? And you’re not even asking us if that’s O.K.?” he asks in the new book. “‘I have always,’ I told him, ‘written about my children,’” Mrs. Viorst writes. “To which Alexander quietly replied, ‘Mom, we aren’t children anymore.’”

It was an important moment. Mrs. Viorst conceded the point. But she forged ahead, promising Alexander she wouldn’t publish the book without his permission. He eventually consented. A photograph of the whole gang — and a drawing of Alexander from his terrible, horrible days — graces the front cover. (Alexander politely declined to be interviewed for this article. “I’m going to take a pass and let my mother be the spokesperson for the book,” he wrote in an e-mail message.)

Book or no book, it’s easy to see why the Alexander Five would have wanted to move back in. Since 1971, Mrs. Viorst and her husband, the political writer Milton Viorst, have lived in a three-story house on a quiet cul-de-sac in Cleveland Park, a hilly, upscale corner of Northwest Washington. Though not ostentatious in its beauty, the house has a laid-back Southern Gothic charm. The white exterior is grand, with a curved row of Ionic columns supporting a wraparound front porch, enclosed by jungle-like vines. Above, there’s a balcony. A small swimming pool is tucked behind the driveway. Across the threshold, a spacious entrance hall with a high ceiling opens onto two facing living rooms. In the back, there’s a sunny dining room and a pantry hallway leading to a cozy, well-appointed kitchen.

The Viorsts fell for the house right away, and bought it for just over $60,000. “My father said, ‘How’s the roof?’” Mrs. Viorst recalled. “I said, ‘Irrelevant.’ He said, ‘How’s the furnace?’ I said, ‘Irrelevant — we’re getting this house!’” She added, “I still come home from an evening out with Milton and the porch light is on and I say, ‘Honey, that’s our house, and we get to keep it!’”

The house feels comfortably lived in — and is. Both Viorsts write from home, in sunny adjoining offices on the second floor. In hers, an apple green desk faces an alcove bookshelf whose bright blue shelves sag under the weight of her own books. The complete works of Sigmund Freud line one shelf (Mrs. Viorst is a graduate of the Washington Psychoanalytic Institute), and photos of her with Woody Allen and Barbara Bush hang on the wall.

On the third floor, with its blue carpet and walls, are the childhood bedrooms of Alexander and his older brothers, Nicholas and Anthony, now in their 40s. Although it has become the grandchildren’s floor, with toys, stuffed animals, crayons and cribs, it still has traces of the past: A Georgetown Hoyas garbage can, some diplomas, a wall of buttons that hark back to the ’80s: “Peace Now,” “Card-carrying member of the A.C.L.U.,” “Boycott Nestl?.”

Generally, though, the d?cor has a ’70s vibe, as if little had changed since the boys scampered around the rooms in which their own children now play. There’s moss-green carpet on the stairs and paintings that look like a cross between Botero and Giacometti on the olive green living-room walls. Tchotchkes and sculptures of animals are scattered around. “I guess it’s obvious that I’ve never used a decorator,” Mrs. Viorst said.

Having a welcoming house was more important, even if her belief in hospitality runs up against her urge for control. Still, she conceded, while the Alexander Five were living with them, “I did surprise myself by hanging looser than I’ve ever held in my life.”