For parents, regulating teens' time on cell phones, tablets and computers is new territory, and many make up the rules as they go along. It's not surprising. Online life is full of contradictions. Kids need their devices for homework, but they are also a major distraction from getting homework done. Social networking sites can give shy and socially awkward kids a place to socialize and be part of a group; they can also be a place of social torment.

A decade into the widespread use of smartphones, tablets and computers, two new studies offer parents a better understanding of how to make the most of the benefits of smartphones and social networks while reducing their downsides.

Young people's life satisfaction, self-esteem and happiness all showed a sharp drop after 2012, the same year that the percentage of Americans who owned a smartphone first rose above 50 percent.

The first study found that the happiest teens are those who spend about an hour a day in front of their various screens. Beyond that, as screen time rises, the study of over one million eighth-, tenth- and twelfth-graders in the United States found, unhappiness rises.

Jean Twenge, the lead author and professor of psychology at San Diego State University, believes that it's screen use that is driving up unhappiness, not the other way around: “By far the largest change in teens' lives between 2012 and 2016 was the increase in the amount of time they spent on digital media, and the subsequent decline in in-person social activities and sleep,” she said. “The advent of the smartphone is the most plausible explanation for the sudden decrease in teens' psychological well-being.”

The researchers looked at information from national surveys teens took yearly between 1991 and 2016, asking students questions about how much time they spent on their phones, tablets and computers, as well as questions about their face-to-face social interactions and their overall happiness.

Online life is full of contradictions. Kids need their devices for homework, but they are also a major distraction from getting homework done.

The study, published in the journal, Emotion, found young people's life satisfaction, self-esteem and happiness all showed a sharp drop after 2012, the same year that the percentage of Americans who owned a smartphone first rose above 50 percent. And while this could be a coincidence, other studies have also found a link between time spent on smartphones and unhappiness.

The connection between phones and adolescents' emotional health is about what teens are — or aren't — doing when they are not on their phone or computer. Teens who spent more time on screen-based activities such as social media, texting and gaming, at the expense of non-screen activities, such as in-person social interaction, sports, exercise and homework, had lower psychological well-being.

“The key to digital media use and happiness is limited use, Twenge advises. “Aim to spend no more than two hours a day on digital media, and try to increase the amount of time you spend seeing friends face-to-face and exercising — two activities reliably linked to greater happiness.”

Make Media Rules that Give Teens Credit

Screen time is not good or bad. It's both, and parents who develop a deeper understanding of their children's use of it are likely to be able to set limits that respect their kids and that their kids will respect. For example a British study of teens' use of social media to get health information came up with some reassuring results. It found that when teens are searching the Internet for information, they are more discriminating about media content than adults often give them credit for.

Parents who develop a deeper understanding of their children's use of online resources are likely to be able to set limits that respect their kids and that their kids will respect.

So rather than encouraging teens to limit their screen time or issuing a blanket demand that they do so, the authors of this study, published in Sport, Education and Society, recommend that parents focus instead on teaching their children how to be better at judging the legitimacy and value of the content they are reading online: “[R]elevant adults can reduce risk and realize more of the positive impacts of social media for young people by focusing on content, and the ways in which content is shaped in the interplay between interactive functionalities of social media (e.g., likes and followers) and young people's social uses of social media (e.g., friends, information).”

Being able to discriminate between a site with information that is based on verifiable research and one that is funded by an interest group or promoting a commercial product is a useful skill that kids can carry into adulthood.

So, yes, there is plenty of health-related misinformation to be found online, but there is no denying that online services and social media help people's health in many ways. For example, online services have made health information and social support readily available; they can even help people keep food diaries.

In addition to paying attention to the quality of content their kids are accessing, parents need to be on the lookout for the times when teens switch from controlling online media to a point where the media is controlling them — something that has probably happened to all of us at one time or another, unfortunately.