The study of 350 children in a low-income, minority community in the US suggests that an income-based 'digital divide' is shrinking.

The study found that tablets are the most popular mobile devices for children, and kids as young as 1 use them more than 20 minutes a day on average.

For the study, researchers gave a questionnaire to parents of children between 6 months and 4 years of age who visited a Philadelphia pediatric clinic in October and November of 2014.

The parents answered questions about the children's use of television, mobile devices, computers and video games.

Almost every household (97 percent) had a TV, 83 percent had tablets, and 77 percent had smartphones. Just over half had video consoles (56 percent), a computer (58 percent), and Internet access at home (59 percent).

The study found that by age 4, about three-quarters of youngsters had their own mobile device, and half had their own TV. All but 3 per cent had used a smartphone or tablet, the study found.

"We were not surprised to see infants and toddlers using the mobile devices; we saw that in the clinic every day," said one of the study's authors, Dr Matilde Irigoyen, chair of pediatrics and adolescent medicine at Einstein Medical Center in Philadelphia.

More than four out of 10 children under age 1 and 77 percent of 2-year-olds used a mobile device every day to play games, use apps or watch videos, the researchers found.

Almost half of 4-year-olds and one-quarter of 2-year-olds needed no help using a smartphone or tablet.

While 28 percent of parents said they used a mobile device to get their child to go to sleep, 70 percent did chores while their child played.