Christmas came and went, and my youngest child did not get the one gift he most wanted.

Despite his disappointment about not yet owning a smartphone, I don’t feel bad – not after reading “iGen: Why Today’s Super-connected Kids are Growing up Less Rebellious, More Tolerant, Less Happy – and Completely Unprepared for Adulthood.” Psychologist Jean Twenge’s new book echoes concerns raised by social psychologist Adam Alter in “Irresistible: The Rise of Addictive Technology and the Business of Keeping Us Hooked,” which I reviewed in a column last spring.

Both books affirm that decisions made about children’s cellphone and social media use are more consequential than we might realize. Sustainable living rests on the premise that choices made today will not harm future generations. We are clearly failing to uphold this standard in many areas, most notably with environmental pollution and excessive resource use. But a less obvious threat to children’s long-term well-being lies – literally – in our hands.

Young people venture into social media and online games at an age when they are self-conscious and lacking in clear judgment. Bad habits formed during this period of rapid growth, neuroscientists report, can get wired into the architecture of developing brains. (There are also growing concerns about what electromagnetic radiation from cellphones does to human brains.)

Adolescents now spend, on average, six hours “leisure” time on screens each day – texting, internet surfing, gaming and video chatting. Half of college students report feeling “addicted” to their phones, an admission that may be frighteningly close to the truth. University of Michigan scientist Daniel J. Kruger found that 80 percent of college students in a recent study experienced “phantom cellphone buzzes” (sensing a vibrational alert to a call or text that had not occurred), a symptom associated with addicts who “become hypersensitive to cues related to the rewards they are craving.”

Smartphones and social media undermine happiness in adolescents, Twenge asserts, documenting evidence (admittedly, correlational rather than causational) of greater depression, loneliness, anxiety and social isolation. Members of iGen,whom she defines as those born after 1995 when the Internet launched, bear the brunt of this impact since most enter adolescence with a phone in hand and a presence online. One college student, observing that she can no longer converse with her younger sister (who sits, head bent over screen, answering in monosyllables), says “I’m saddened by the fact that our online lives have become more important than our real ones.”

For those of us who share that concern, what can be done? We might start by challenging the sugar-coated view of social media as a great connector, a means to reunite with long-lost friends and foster new ones. These platforms were never designed with that goal in mind, as Facebook founding president Sean Parker recently confirmed. Characterizing himself now as “something of conscientious objector,” he admits that the driving impulse behind these platforms was “How do we consume as much of your time and conscious attention as possible?”

Their success is evident in levels of distractedness almost unimaginable in previous generations. One study that involved a computer program taking screenshots every 19 seconds of college students’ laptops found that 75 percent of the windows they viewed were open less than one minute. Relentless mental racquetball – bouncing among Instagram, Snapchat, Spotify and YouTube – is hardly conducive to the sustained focus needed to tackle professional and societal challenges.

The last two years have demonstrated vividly how social media can deliberately distort news and information, fostering extreme partisanship and making reasoned discussion of differences more difficult. “Where iGen goes, the country goes,” Twenge warns. If today’s youth are lost to the social media and online gaming vortex, it does not bode well for our democracy or our world.

Fortunately, other signs of resistance are surfacing. Earlier this month, two significant Apple investors sent the corporation a letter asking for changes in its operating system that would make the phones less addictive. Current parental controls on cellphones and computers are inadequate at best and complex, costly and ineffectual at worst. Apple could design its initial registration process so that parents could restrict apps, set shutdown times and limit daily hours.

Technological changes may inch us slowly toward a better balance with the virtual world, but Twenge’s book suggests another path to adopt immediately. As parents and citizens, we can start rekindling personal interactions and engaging young people in projects to benefit others and the earth. That might be the most lasting gift we can offer today’s children.

MARINA SCHAUFFLER provides research, writing, and editing services to nonprofit and social enterprise organizations through Natural Choices (naturalchoices.com).