Real bad. We may need to want them more.
Further to why screen addiction matters to children, we should be aware of how much billionaire companies have invested in captivating them.
Consider this, for example, from California Sunday:

“You don’t know where you are or when you are with this show, so it’s timeless,” he says. “I love that quality.” Siegel, who’s 14, speaks without a trace of slang; dressed in the episode’s magical blazer, with his thick hair parted on the side, he, too, seems timeless. Gortimer is one of a slate of original children’s shows being produced for Amazon Instant Video, which, along with other streaming services, is dumping money into content for children. Kids watch a lot of TV, which increasingly means watching a smartphone or tablet — in 2013, according to Common Sense Media, 75 percent of u.s. children aged 8 and younger had access to a smart mobile device in their homes. This, combined with young kids’ habit of playing favorite episodes again and again, gives video-on-demand networks such as Netflix, Amazon Instant Video, and Hulu Plus a big advantage over traditional broadcast and cable networks. Executives see an opportunity to shape a new generation’s viewing habits, as well as to turn parents, eager to entertain their kids with nonjunk, into subscribers.
Of course, the problem is that just because something isn’t mere Little Lulu cartoons doesn’t mean it is harmless. Nonjunk can be harmful precisely because messages are more likely to shape attitudes than nonsense is.
And there’s a market:

In late 2013, a Nickelodeon survey found that children aged 9 and younger watched an average of 35 hours of television per week, a 2.2-hour increase from 2009. That’s in addition to other screen time like gaming and surfing the web. According to the American Academy of Pediatrics, the average 8-year-old spends eight hours a day — 56 hours per week — using electronic media such as laptops, tablets, and smartphones. “Go to the airport and you’ll see a 2-year-old who knows how to operate Netflix on his iPad perfectly,” Sarandos says.

The number of children’s networks kept multiplying through the 2000s, and today there are more than 400 networks catering to children worldwide. As a result, they have staked out ever-narrower demographic niches — 6-to-11-year-old boys, 12-to-17-year-old girls — that they can market to advertisers. This narrowing effect, plus attempts by networks to replicate past successes, has led to a lot of formulaic shows. In recent years, Nick’s sitcoms, like How to Rock and Marvin Marvin, have been criticized for relying on pratfalls, stereotyped characters, and potty humor. “I can’t tell if there’s a set of informing ideas that guide [Nickelodeon today], except We’ve got to make money for Viacom,” says Scott Webb, who served as Nick’s first creative director. Without advertisers to worry about, Netflix and Amazon can make ambitious kids’ shows that appeal to a more eclectic viewership, more like movies. And even ambitious children’s programming is cheaper than similar shows for adults, thanks to smaller casts, mostly unknown talent, and a general belief that kids are less discerning when it comes to production values. More. 
Kids are less discerning about values, period. They haven’t usually lived through their consequences. So one needn’t be a fusspot or concern troll for wondering about all this.
For example, fifty years ago, respected major manufacturers’ made sugared breakfast cereals a staple in North America. Everyone loved them except dentists and school health nurses.
And the dentists and school health nurses were right. The worst argument I ever heard for any product ever was made by their defenders in Canada. They argued that many children would at least eat breakfast if much of the cereal was sugar.
Yes, of course they would. But that didn’t make a possible lifetime addiction to sugar highs an asset to their health.
So, just as I wouldn’t have allowed my kids to stuff themselves with sugar highs while dumped out in front of just any old 1970s TV show that met minimal public broadcast standards, no parent today should assume that their kids should roam these new services without oversight. See also: Can smartphones make children borderline autistic? What about teens? Living online may mean that social cues, skills, and smarts deteriorate.
Should we restrict children’s/teens’ Internet use? Taiwan is doing so (and ranks high in education success).
Why Steve Jobs was a low tech parent, and why it isn’t really all that surprising Children are at risk for Internet addiction because, unlike substances, it isn’t controlled, except by parents or teachers. Note: Cane sugar isn’t a controlled substance either. That doesn’t mean it is an important part of a healthy diet, as opposed to an occasional treat.

Denyse O’Leary is a Canadian journalist, author, and blogger.