The craze for tablets and smartphones is spreading to ever younger users.
A new study of American households found 38 per cent of children younger than two have used a mobile device such as a tablet or smartphone, compared to 10 per cent in 2011.
The study, by Common Sense Media, said children up to age eight still spend more time with "traditional" screen media such as TV, DVDs, computers, and video games, but that this is shifting.
Overall screen time is down by 21 minutes, with mobile time up 10 minutes, the study found. Viewing on a television set still makes up half of all screen time.
"In the past we could measure and control exactly where, when, and how they were engaging with screens. Now, mobile devices follow our kids from room to room," James Steyer, Common Sense Media chief executive, said.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
"The media children consume can have a profound impact on their learning, social development, and behaviour, and the only way to maximise the positive impact - and minimise the negative - is to have an accurate understanding of the role it plays in their lives."
The average amount of time children spend using mobile devices has tripled, from five minutes a day to 15 minutes a day for the zero-to-eight age group, the study found, and the number of children who have used mobile devices has nearly doubled from 38 to 72 per cent.
The most common mobile media activity among children is playing games, cited by 63 per cent of parents.
Some 30 per cent also used devices for reading.
The report is based on a survey of 1463 parents of children age eight and under, including an "over-sample" of African-American and Latino parents from May to June.
