When her children were ready to have laptops of their own, Jill Ross bought software that would keep an eye on where they went online. One day it offered her a real surprise. She discovered that her 16-year-old daughter had set up her own video channel.

Using the camera on her laptop, sometimes in her bedroom, she and a friend were recording mundane teenage banter and broadcasting it on YouTube for the whole world to see.

For Ross, who lives outside Denver, it was a window into her daughter’s mind and an emblem of the strange new hurdles of modern-day parenting. She did not mention it to her daughter; she just subscribed to the channel’s updates. The daughter said nothing either; she just let Mom keep watching.

“It’s a matter of knowing your kids,” Ross said of her discovery.

Parents can now use an array of tools to keep up with the digital lives of their children, raising new quandaries.

Is surveillance the best way to protect children? Or should parents trust them to share if they are scared or bewildered by something online?

The answers are as varied as parents themselves. Still, the anxieties of parenting in the digital age have spawned a mini-industry, as startups and established companies market new tools to track where children go online, who they meet there and what they do. Because children are glued to smartphones, the technology can allow parents to track their physical whereabouts and even monitor their driving speed.

If, a few years ago, the emphasis was on blocking children from going to inappropriate sites on the family computer, today’s technologies promise to embed Mom and Dad — and occasionally Grandma — inside every device that children are using and gather intelligence on them wherever they go.

A smartphone application alerts Dad if his son is texting while driving. An online service helps parents keep tabs on every chat, post and photo that floats across their children’s Facebook pages. And another scans the Web in case a child decides to try a new social network that the grown-ups haven’t even heard of yet.

Devices everywhere

The spread of cellphones and tablets in the hands of children has complicated matters, giving rise to applications that attract the young and worry parents. Earlier this month, for instance, came revelations that an app designed for flirting, called Skout, had led to three sexual assault cases involving children across the country.

The average U.S. family uses five Internet-enabled devices at home, including smartphones, a recent survey by Cox Communications and the National Center for Missing and Exploited Children found, while barely 1 in 5 parents uses parental controls on those devices.

In Richmond, Va., Mary Cofield, 62, is one of the careful ones. She struck a deal with her 15-year-old granddaughter last year. The girl was offered an Android phone with full Internet privileges, so long as Grandma could monitor her every move.

Cofield, a retired government tax agent who runs an online travel business, chose a tool called uKnowKids.com, which combs the granddaughter’s Facebook page and text messages. UKnowKids sends her alerts about inappropriate language. It also offers Cofield a dashboard of the child’s digital activities, including what she says on Twitter, whom she texts and what photos she is tagged in on Facebook. It translates teenage slang into plain English she can understand.

Often, she says, she gleans when the girl is having trouble with a boy or when there’s conflict among friends. Most often, Cofield knows to keep her mouth shut.

“Being privy to that information and not using it is also difficult,” she confessed. “If I did that, she would definitely go underground. I would be hopping on her every day.”

Surveys, including by the Pew Research Center, have found that two-thirds of parents do check their children’s digital footprints and nearly 40 percent follow them on Facebook and Twitter. But the Pew study suggests that this monitoring is also likely to lead to arguments between parent and child.

What’s more, technology is at least as nimble as adolescents, and neither parents nor the technology they buy can always read a teenager’s mind. Sometimes children deactivate their Facebook accounts except at night, when they know their parents are not likely to be logging on. They roll over to new sites, often using pseudonyms. Very often they speak in code designed to stump parents.

All ages

Technology companies now market tools for parents of children at every age group. The next version of Apple’s mobile operating system will offer a single-app mode so a parent can lock a toddler into one activity on an iPad.

Security companies like Symantec and Trend Micro offer computer software that detects when a child tries to visit a blocked website or creates a new social network account. Infoglide, based in Austin, Texas, whose bread and butter is making antifraud software, recently introduced a tool called MinorMonitor, which like UKnowKids mines children’s Facebook pages for signs of trouble.

Independent measurements of the market for family safety tools are hard to come by, and most companies do not release sales. But that the market is large — and growing — is evident in two things: Every security company and cellphone carrier is pitching such products, and startups in this field are popping up every month.

A text message application for the iPhone called textPlus allows Kyle Reed of Golden, Colo., to be copied on every text message his teenage son sends his girlfriend.

“I feel torn a little bit. It’s kind of an invasion of privacy,” he said. “But he’s 13. I want to protect him.”

Dan Sherman of Jackson, N.J., is what you might call the alpha monitor of his children’s digital lives, which is not surprising considering that he works in computer security.

At home, he has installed a filter that blocks pornographic sites and software that tracks Web visits. He has set parental controls on the iPhones of his 8- and 13-year-old daughters so they can’t download applications. Access to the app store on the 8-year-old’s Kindle Fire is protected with a password. And the older daughter’s Facebook account is tracked by MinorMonitor, which alerts Sherman if there are references to bullying or alcohol.

Does he worry that his daughters think he doesn’t trust them? Sherman says they should learn that they will be monitored throughout their lives: “It’s not any different from any employer.”

The older daughter, Alexis, said that for now, at least, she doesn’t mind the monitoring. She feels safer for it, she says, “like I’m being watched over.”

She also knows that it affects what she posts for public consumption. Recently, for example, she was tempted to rail on Facebook against a friend who had spread rumors about her at school, but she checked herself when she thought about what her mother might say.

“Having your parents monitor makes you think twice about what you put,” Alexis said.