Three-quarters of 4-year-olds in a low-income minority neighborhood in Philadelphia had their own smartphone, iPod or tablet and most used them without help, according to a report published on Monday.
Three out of four parents gave the devices to their children while they were doing household chores and to keep their children calm, and a quarter to put their children to sleep.
"Little is known about how children’s independent activity on mobile devices affects their cognitive, social, and emotional development," the study noted.
Nearly all children began using mobile smart phones or tablets before they were a year old, the study published in the journal Pediatrics found. Almost half played games or watched videos every day.
By the time they were 2, most children used them mobile devices daily and spent about the same amount of time on the devices as on television.
One third of 3- and 4-year-olds used several media devices at the same time, the study found. YouTube and Netflix were popular.
"Our study found that household ownership of tablets doubled since 2013, reflecting the pervasive nature of digital technology," the authors wrote.
According to Common Sense Media's nationwide survey, 72 percent of children age 8 or younger used a mobile device, up from 38 percent in 2011.
U.S. & World
In 2013, ownership of mobile devices among children 8 and younger was in the single digits and only 17 percent of 2-, 3- and 4-year-olds reported using mobile devices every day, the study noted.
The study covered 350 children ages 6 months to 4 years who were seen at a pediatric clinic in Philadelphia between October and November of 2014.
It noted that a child's skill with mobile devices was a first step toward digital literacy. But it also cautioned that socialization with parents was critical for developing healthy ways to integrate technology into family life.
The American Academy of Pediatrics had urged parents to limit screen time to two hours per day for children over age 2 and discouraged screen time for younger children. More recently it released guidelines that address how to use technology with children.