When Jennifer Schuur Herbert passes a rack of tabloid magazines in her Los Angeles neighborhood, she is often reminded of what can happen in even the most glamorous Hollywood marriages.

“He Cheated With Their Nanny!” trumpets the Nov. 23 cover of Us Weekly, with a glamour shot of Gwen Stefani and the promise of details of how her former husband, Gavin Rossdale, the lead singer for the band Bush, had a three-year fling with Melinda Mann, the babysitter for their three sons.

This cover comes just three months after the magazine printed photos of Ben Affleck and Jennifer Garner, looking dour, with one of Christine Ouzounian, the winsome 28-year-old who had cared for their three children, along with the ominous phrase: “He’s Dating the Nanny!”

At least since Rebecca De Mornay starred in “The Hand That Rocks the Cradle,” the nanny — once a no-nonsense figure in starched petticoats, à la Mary Poppins — has been regarded in the popular imagination as a potential home wrecker.

Real-life stories, alas, have born out this primal fear: Robin Williams divorced his first wife in 1988 and married the babysitter, Marsha Garces. (Ms. Garces divorced him in 2010.) Ethan Hawke divorced Uma Thurman in 2005 and married their children’s nanny, too. Later, Jude Law split with his fiancée, Sienna Miller, after an affair with his children’s nanny.

Ms. Herbert, happily married for four years with two children and a nanny to oversee them, said it has crossed her mind that her husband may one day find a sitter attractive. But, she said, if she and her husband are worrying about whether a nanny is too hot to hire, there are bigger problems afoot.

“I come at it from a pretty practical place,” said Ms. Herbert, who is a television writer and producer. “If my husband has a wandering eye, he has a wandering eye. And I can’t guard against that.”

But some famous wives have been trying to recruit caretakers with an eye toward reducing temptation — perhaps realizing that the nondisclosure agreements that have become standard among the wealthy do not protect them from embarrassing photos posted on the Internet, like those of Ms. Ouzounian riding on a private jet to Las Vegas with Mr. Affleck or in the pool at the Hotel Bel-Air.

“We get those requests all the time, ‘I don’t want someone pretty,’” said Katie Provinziano, the founder of Westside Nannies in Beverly Hills, Calif., an agency that places nannies with celebrity clients. “People are picky. They tell you what they want.”

As on dating sites, they sometimes also rule out candidates based on weight. “They don’t want someone who looks out of place with the family,” Ms. Provinziano said.

“But we can’t discriminate based on those factors,” she said. “It’s our job to take that mom and tell her, ‘You can’t have that conversation.’”

Kenya Hathaway, a musician and vocal coach for television shows, has never talked with her husband about celebrity nannies, even in light of the unraveling marriages of the Afflecks and Rossdales.

“I’m not a supermodel and he knows that, and he’s the same way,” she said. They hire a nanny for their two daughters only when they are both working, and that person does not live in their home.

Still, it is not uncommon to hear stories, she said, including from nannies themselves. “I’ve had nannies who have said they were scrutinized and told to tone it down,” she said. “That’s horrible that wives feel a little bit threatened.”

Devon Bookman, 27, a former nanny in Los Angeles, said she used to play down her looks when going to an interview, wearing conservative khakis from Old Navy, natural makeup and her hair up, she said, “so I didn’t look like a blond bombshell.” Only after knowing the family for six months would she wear something casual, like skinny jeans.

Lindsay Heller, a.k.a. the Nanny Doctor, a clinical psychologist who is a consultant to families and their nannies, has counseled several couples whose husbands have cheated with a younger, attractive nanny. “If a parent is lacking in the relationship with their partner or wife, all of a sudden they have someone making their breakfast, and talking about picking up the kids,” she said. “I’ve seen people who won’t hire a hot nanny because they are worried about what their husbands will do.”

She added that many celebrity or wealthy mothers prefer older nannies not out of jealousy, but because they want a professional uninterested in becoming a member of the Gulfstream entourage or using the job as a steppingstone to becoming an entertainer.

“There are nannies whose identities get lost and absorbed into their jobs,” Ms. Heller said. “They think they should be living a lifestyle that they have become accustomed to.”

One woman who works at a media company in Los Angeles but declined to be named to protect her family’s privacy said she hired a young nanny for a two-day tryout but decided not to give her a full-time job because the nanny had been taking care of a singer’s children on tour and wanted the fast-paced, go-go lifestyle of a rock star.

“That wasn’t going to work,” she said. “We live in suburbia.”

Instead, she hired a 50-something woman with children of her own who worked for a family for 16 years. “She doesn’t want to be a mom and she doesn’t want to sleep with my husband,” said the woman, who has a toddler. “She has a family in Long Beach. We wanted someone with a life of her own.”

When a sitter does contribute to a split, though, Ms. Heller said she encourages children to create a “goodbye” book to give to the nanny and come up with a rehearsed answer if asked if their parents are getting divorced.

“It is worse in Hollywood because it’s in every single magazine on the newsstand and kids talk about it at school,” she said. “Their loyalties are split and they are confused.”

The rising class of Silicon Valley parents up north, meanwhile, professed disinterest in such tabloid dramas.

“We don’t really think about it,” said Brit Morin, the founder of Brit & Co., a craft and editorial website in San Francisco. She hired a nanny for her son, Ansel, through an agency.

But in the Bay Area and elsewhere, the business of child care has been co-opted by online services like Care.com or Urbansitter.com that resemble Tinder for the nanny set, with head shots, ages and capsule descriptions of interests.

“People are lured by the ‘Uber’ nanny,” said Daryl Camarillo, the founder of Stanford Park Nannies, which, along with Town & Country, is well respected among technology executives. “They go ‘click click,’ and they see someone that looks nice and think, ‘Now I can get back to work.’”

At Stanford Park, she said, nanny candidates are vetted, with only one out of 10 applicants added to the roster. Families are schooled that when a nanny is present, the home is a workplace. (“That’s so Dad doesn’t walk downstairs in his underwear,” she said.)

“When we present candidates, we don’t present a photo,” Ms. Camarillo said. “So there isn’t an opportunity for people to say: ‘Whoa, she’s awfully pretty. We don’t want her to come.’” Besides, she said, “if the mom is concerned about what the nanny looks like, she should ask herself why she feels that way and look inside her marriage before hiring anyone.”

And, as Ms. Provinziano of Westside Nannies put it, don’t blame it all on the babysitter. “If cheating is going to happen, it’s going to happen,” she said, “whether it’s the nanny or not.”