(Bee Johnson/For The Washington Post)

When my regular babysitter went on vacation, she suggested I hire her younger, 15-year-old sister, who had previously worked for me as a mother’s helper.

The morning after our new sitter watched our 7-year-old daughter, I heard how it went. “We had fun, Mom,” our little girl said. “And right before I went to sleep, I talked to a nice, brown-haired boy.”

I felt a frisson of panic run though my body. “What do you mean? Did someone come in the house?”

“No, I saw him on her phone, on FaceTime, like how we talk with Daddy when he’s on a business trip.”

My husband and I have worked hard to protect our daughter from too much screen time, keeping her away from social media and the dangers of strangers interacting with her. The idea that my daughter had video-chatted with a boy I didn’t know felt as if a stranger had been in our house, sitting on the couch with our young daughter. I felt unsettled.

(Bee Johnson/For The Washington Post)

When I asked the sitter about it, she said her friend had FaceTimed her with a question about homework. Her voice was matter-of-fact as she explained something that is obviously second nature to her — and to most teens today.

“This can’t happen ever again,” I said, and then explained: “I don’t want her talking to or meeting anyone I don’t know in person or online, and I don’t want anyone to see my home that way, either.”

Our sitter apologized and said it wouldn’t happen again, but it made me see how normal this was to her and my daughter.

Most parents who hire caregivers know the importance of babysitting safety. They instruct caregivers to adhere to bedtimes, make sure the kids eat a vegetable at dinner, don’t let them cross the street without holding a hand. But few parents realize how smartphones, tablets and apps can affect their children’s safety right in their own home. And it’s not just about safety: Many sitters rely on screens to entertain kids when parents have rules against it.

According to statistics in a babysitter survey by Care.com, 26 percent of families have caught their sitter texting, and 22 percent have caught them playing on social media when they were supposed to be watching their charges. Social-media issues now trump the smaller 11 percent of parents catching their sitters having a friend over or looking through their drawers.

Sitters may have good intentions when introducing children to games, social media and geotracking activities, such as Pokémon Go, but they may not be considering the consequences. Although in­cred­ibly rare, one innocent mistake, such as posting and tagging a photo of your child or checking in at a park, could result in an online predator finding your child’s location. In fact, Pokémon Go was recently found to deliver kids directly to sex offenders’ homes.

Although Instagram’s geotagging system can be disabled, it can easily be turned back on by accident, alerting people to your child’s every move. And if a sitter posts a photo of your child doing something wacky, it could go viral, as has happened, playing havoc with your family’s serenity.

Just as with any other instructions they give a new sitter, parents should also outline their rules for social-media use.

“Communication is your best weapon,” says Kim Estes, child-safety expert and founder of the website Savvy Parents Safe Kids. “It’s also important for you to realize that sitters — particularly young teens — are not trying to be sneaky. There is a modern-day generational technology gap. They think it’s normal to share everything online, and we don’t. Because they don’t share the same values as us and don’t see it as a danger, we need to be clear with our expectations.”

That communication extends to children, from a very young age, as well. Talk to them about family rules and how they are in place to keep them safe, and then adjust as necessary as they get older. Then, when a sitter comes over, give your children “a gentle reminder in front of the sitter to ‘remember our family safety rules,’ ” Estes suggests. “This way your child will know that he or she can refuse to do something that breaks the rules, even if the sitter suggests it.”

Add Snapchat to the growing list of social-media apps that might cause problems. Many sitters enjoy using it with kids because of its fun face filters. The danger with the app is that because photos and videos disappear after a maximum of 10 seconds, it feels temporary, but all it takes is a screen shot for a picture or message to live forever.

Colleen Bohensky, a New Jersey mom, saw photos of her friend’s 8- and 6-year-olds on Snapchat after that friend’s babysitter posted them. “I was the one who saw the photos,” Bohensky said. “I swiped on the pics and messaged her about how cute her boys looked.” Her friend, who had a strict no-social-media rule, was upset. She’s planning to speak to her sitter but is unsure what to do. She doesn’t want to have to follow her sitter on social media to be sure that she isn’t posting pictures of her kids. “It’s unfortunate, because she is an amazing sitter otherwise.”

Social-media usage is a key subject to address with a sitter, says Genevieve Thiers, founder of the online child-care company Sittercity and the babysitter-booking app Chime .

“Cut it off at the pass,” she suggests. “Say, ‘Please don’t share pictures of my kids, and don’t show them social-network screens.’ ”

And if a sitter puts a photo on social media and you find out about it? “Immediately call (don’t text) and ask them to take it down,” she said. “Explain why it is important and that it is a nonnegotiable.”

Estes is a fan of Circle With Disney, a $99 tool that allows you to set limits on what children can access online and to monitor access to all devices on your home network.

Lynn Perkins, founder and chief executive of UrbanSitter , agrees that it’s up to parents to set boundaries. “When meeting with a new babysitter, you will want to walk them through your child’s routine and get them familiarized with your home,” Perkins says. “Some of the parents who use our service say, ‘Please only use your phone in case of an emergency, if you need to text me a question or when the child/children is asleep.’ Others ask sitters to keep their children off of their social-media feeds. And then there are the parents who say it’s okay to take photos or videos to send to the parents, but then they have to be immediately deleted. ‘And don’t tag people or locations or use my kids’ names or our last name.’ ”

Jo Frost, formerly known as “Supernanny,” is practical about digital abuse. “Like we overused playpens in the 1980s and 1990s by sticking our children in them, today we are misusing technology as an electronic babysitter. But since it is here to stay, we need to embrace it, regulate it and use it in moderation,” she said in an interview.

It’s fine for nannies to use the phone for emergencies or to take a funny photo or video and send it to the parent, she said, but they need to be hands on with children and use their imagination and creativity to entertain them. “It’s not okay to use devices as a sitter for kids. It takes them out of the moment.”

Parents are still feeling their way when it comes to making rules about babysitters and social media. Because the field is so fluid, with new apps developed every day, it’s hard to tell what we are going to be dealing with in the future.

“No matter what, it’s essential to protect children — particularly young children — from situations that they have yet to learn to be discerning about and can’t make choices on,” says Irina Harris, a New York-based therapist. “You have to decide what your rules are on the use of devices and apps, then you have to convey them to the sitter, plus spell it out to the child in simpler terms. It all takes a bit of work.”

I told Harris that after the FaceTiming issue, I let everyone know that our house safety rule is “Nobody in, nobody out, and that includes on social media.” My sitters and my daughter need to understand that if someone comes into my home digitally, it is the same as letting them in the front door. And that’s not okay.

Estelle Erasmus is a journalist, author and writing coach. You can find her on Twitter @estelleserasmus