The children’s commissioner has warned parents that they must intervene to stop their children overusing social media and consuming time online “like junk food”.

As web use reaches record highs among children, Anne Longfield has attacked the new methods social media giants are using to draw them into spending more time staring at tablets and smartphones. In an interview with the Observer, she said that parents should “step up” and be proactive in stopping their children from bingeing on the internet during the summer holidays.

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Launching a campaign to help parents to regulate their children’s internet use, she said time online should be balanced in the same way that parents regulate their children’s diets. “It’s something that every parent will talk about especially during school holidays – that children are in danger of seeing social media like sweeties, and their online time like junk food,” she said.

“None of us as parents would want our children to eat junk food all the time – double cheeseburger, chips, every day, every meal. For those same reasons we shouldn’t want our children to do the same with their online time.

“When phones, social media and games make us feel worried, stressed and out of control, it means we haven’t got the balance right. With your diet, you know that, because you don’t feel that good. It’s the same with social media.”

Her warning comes after a report said that children in all age groups are spending ever-longer periods online. The internet overtook television as the top media pastime for British children last year, according to the media regulator Ofcom. Children aged five to 15 are spending 15 hours a week online.

Last year the time three- and four-year-olds spent online increased from six hours 48 minutes to eight hours 18 minutes a week, while 12- to 15-year-olds now spend more than 20 hours online.

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Longfield said children should be helped to understand that sites encourage them to click on another game or video based on what they had just played. She had been pressuring Facebook to make it easier for children to report things they are worried about or switch off certain features.

She also criticised a feature on Snapchat, known as the Snapstreak, that she said encouraged children to increase their internet use. A streak is created when friends share photos over three consecutive days, but it is destroyed if a day is missed. Longfield compared the feature to a chain letter.

“You find children saying to parents that they have 30 people that they have to do every day and if they don’t, they drop the streak, and everyone will see,” she said. “And then – does that mean they don’t like me any more? It’s almost like chain letters. There are children who say they can’t not be online, and I think that’s really worrying.

“I want Facebook and all the other social media companies to be as proactive as they can about creating a good place and a safe place for kids to be. At the same time I want them to stop using the algorithms and the targeting that get kids addicted – all those things that we know can be very stressful and very destructive. However, it doesn’t mean that parents themselves can step aside and wait for that to happen.”

Longfield said it was not helpful to recommend an absolute time limit on how long children should be online. Instead, she is announcing a “digital five-a-day” campaign, designed to advise parents and children on a healthy online diet. Rather than switching off the wifi, parents should help children to use their internet time to learn new skills, interact positively with friends and be creative.

The Observer view on keeping children safe in a smart-tech world | Observer editorial Read more

“We’re not saying it’s parents’ fault, or that they should tell their children what to do, because ultimately this is part of life. All of those kids will have grown up with that being the normality. But we do think there is a role here for parents to step up, to stop waiting for others to come up with the solution, be that government or [social media] companies. We want [children] to feel informed, confident and empowered, and have the confidence to say, ‘no, I’m not going to do that’. That same confidence we want for children, we want for parents, too.”

She said Facebook and other social media giants “are not coming forward at quite the speed I would like them to” on making it easier to protect children.

“There is so much more they could do,” she said. “These are clever, clever people, who know their industry well, their tech abilities well. They can do things if they want that I don’t even know exist, and there are some very good examples of them using their expertise, for example by spotting people who have suicidal tendencies. But they are not doing [enough] yet.”

Snapchat and Facebook declined to comment.