Children aged five to 16 spend an average of six and a half hours a day in front of a screen compared with around three hours in 1995, according to market research firm Childwise.
Teenaged boys spend the longest, with an average of eight hours.
Eight-year-old girls spend the least - three-and-a-half hours, according to the study.
Screen time is made up of time spent watching TV, playing games consoles, using a mobile, computer or tablet.
It finds that teenaged girls now spend an average of seven-and-a-half- hours watching screens, compared with 3.5 hours of TV viewing in 1995.
Younger children fare slightly better in 1995, five- to- 10-year-olds averaged around two-and-a-half-hours of TV.
Children's TV viewing habits have changed dramatically, with the majority now watching television via catch-up services and YouTube rather than the traditional TV set, according to the report.
Children are also now multi-screening - using more than one device at the same time, for example, watching TV while surfing the internet on a tablet or mobile so some of the screen time will be concurrent.
"The main difference from the 1990s is that then TV and magazines were the main ways for connecting kids to the media and now they have different devices from tablets, mobiles, games consoles and they have a much higher screen time,
Paid-for on-demand services, such as Netflix, have also risen rapidly in recent years and are expected to continue to grow in popularity.
The study also looks at how the internet has changed the way children engage with information.
"The internet is pivotal to their lives and they are now able to access a wealth of content," said Mr Nevard.
The internet has given children more freedom to explore their own interests rather than being tied into the content offered to them from the TV schedules or magazines.
"They can find the content that they want," he said.
The study describes connectivity as "a fundamental need for young people now".
"Children now don't remember a time before the internet," said Mr Nevard.
Ubiquitous online access is also likely to influence the way children interact with their families and "their willingness to participate in family holidays and trips out", the report finds.
YouTube has remained in the top three since 2007 while Facebook has seen its appeal dip in recent years, as children turn to newer services such as Snapchat.
Children enjoy the privacy of WhatsApp and Snapchat, according to the survey, and the use of such services is also changing how they communicate.
"It reflects the image culture which has emerged, where pictures are utilised to give a better representation of current moods and or activities," the survey said.
http://www.bbc.com/news/technology-32067158