It's an often repeated warning that children who sit in front of the television get 'square eyes', but now parents have a new cause for concern.

The amount of time children spend online has overtaken the time they spend watching television, new figures show.

Children across the UK, aged between five and 15, now spend around 15 hours surfing the web each week compared to around 13 hours watching television.

This is over an hour more per week than last year and the first time online usage has overtaken the amount of time children spend in front of the television, according to Ofcom.

Children as young as three now spend over eight hours a week online.

However, despite the new figures, nine in 10 children still watch TV, generally every day and between 6pm and 9pm.

But increasingly our children's love of television has started to be replaced by YouTube, which has become one of the most popular online sites for children to watch content.

Almost three quarters of five to 15-year-olds now watch the video site, typically for TV-style cartoons and mini-movies.

Even among pre-schoolers the site is popular, with over a third of children yet to reach school age visiting the site regularly.

The data also revealed that over a third of pre-schoolers own their own media device such as a tablet or games console.

However, as children get older they show a preference for smartphones over tablets, with eight in 10 of 12 to 15-year-olds now having their own smartphone.

Ofcom director of market intelligence, Jane Rumble, said: 'Children's lives are increasingly digital, with tablets and smartphones commanding more attention than ever.

'Even so, families are finding time for more traditional activities, such as watching TV together or reading a bedtime story.'