(CNN) -- A new report found the amount of time young children in the United States spend on mobile screens has tripled in just four years, CNN reports.
The report found that while children 8 and younger spent about 15 minutes a day on a mobile screen in 2013, they now spend about 48 minutes a day with them. The report also found that 42 percent of children 8 and younger now have their own tablet devices, which is a large increase from just 7 percent four years ago, and less than 1 percent in 2011.
Douglas Gentile, a psychology professor at Iowa State University, said the findings should not come as a shock.
"On the one hand it's not surprising because it's what we look at around ourselves and can see," he said. "I can see it at the airport, for example, I can see it at restaurants and I can even see it in my own home where my younger daughter watches almost no television but she'll watch lots of TV shows on her phone."
However, Gentile said there are drawbacks to the screen time.
"It's been getting harder for parents to really monitor a lot of what their kids are seeing and doing. At the same time, they're relying on the seeming benefit of being able to quiet the kid at a restaurant with a device. We may be building a bit of a Frankenstein's monster because we're using that power for our benefit, not for the child's benefit."
James Steyer, CEO and founder of Common Sense Media, the company behind Thursday's report, said the amount of screen time has to do with new findings of how many devices are in family's homes.
"One of the most staggering findings is that mobile devices are now as common in the home as TVs -- 98 percent of households with kids under 8 have a mobile device," said Steyer. "The ubiquity of mobile is changing childhood."
The report also found that children 8 and young spend an average of two hours and 19 minutes a day with screen media.
"The report actually shows that kids' overall media use has stayed about the same since our 2011 report. What's changed is how they're using it," Steyer said. "Mobile is totally taking over -- it now makes up 35 percent of screen time, compared to 4 percent in 2011."
The report said children 8 and younger now spend more time on mobile screens than they do reading or being read to, which on average is about 30 minutes a day.