She said one company had told her that current age verification technology was appropriate for them because they needed users to get online “seamlessly”. “But why should it be? If it’s a choice between children having to wait a small amount of time to get on to a site, and continuing to allow them on sites they shouldn’t be on, then to me the answer is obvious,” she added.Ms Longfield backed The Daily Telegraph’s campaign for a statutory duty of care, which is to be introduced by the Government.She said the companies should start introducing the changes now, rather than waiting for the Government’s planned legislation.She is incredulous at their claims that they don’t have the technology to do it and that they are obfuscating by claiming they want people to be able to go seamlessly online without checks. “Instead of trying to hold up the inevitable, it would be wise to get ahead of the curve,” she said. The Children’s Commissioner has mocked the social media firms who claim they cannot block under-13s from their sites but have the technology to see inside black holes.Anne Longfield says it is “particularly frustrating” the tech giants repeatedly claim it is “impossible” to exclude under-aged children because there is “no reliable form of age verification technology”.In an article published on the Telegraph website, she writes: “Can it really be the case that they can create driverless cars, see inside black holes and programme computers to beat the best human players of complex games like Go, but not find ways of making digital platforms fit for purpose for children? “Of course not. And for the record, I’ve been reassured that it is all very possible.” Ms Longfield says it is right, as proposed under a new “game-changing” statutory code, that social media sites such as Facebook and Instagram should be required to block under-13s or face punitive fines. This code could be the first step in redressing the balance,” said Ms Longfield. “Of course, it would be surprising if there was not a flurry of pushback from the tech companies, as so often happens when industry is asked to change its ways. “We will be told it would take a very long time, that it will negate the experience of the activity or that it simply can’t be done.” Show more Under the age-appropriate code, which is due to become law this year, the companies will have to introduce effective age checks, or treat all their users like children.Those that fail to do so risk fines of up to 4 per cent of global turnover, equivalent to £1.5 billion for Facebook. “For too long, the balance of power between children and the platforms they use has been firmly fixed in favour of the latter. Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings.