Fifty per cent of British 10-year-olds use smartphones, according media regulator Ofcom.
The report also showed that by the age of 12 to 15, the percentage of children using smartphones rises to 73 per cent.
"The mobile phone is the device of choice for children," said Yih-Choung Teh, strategy and research group director at Ofcom. "I'm conscious that for these children who have never known a world without the internet, in many respects their online and offline worlds are indistinguishable."
Ofcom also found that 24% of 3 and 4-year-olds had their own tablet, and 15% of them were allowed to take it to bed.
Are smartphones bad for children?
Many of these children with smartphones are still at school, so it's claimed that smartphones distract from lessons, put children's safety at risk, are used to bully and can cause mental harm.
But many parents realise there is no alternative and know that they could risk isolating their children if they have no access to mobile phones.
Ofcom said: "Parents and carers are becoming more likely to trust their children with greater digital independence at a younger age.
"But far fewer believe the benefits of their child being online outweigh the risks than five years ago. And around two million parents now feel the internet does their children more harm than good"
So what are the benefits?
The report also found that more older children were using social media to express their support for social causes and organisations, with 18% having shared or commented on a post, and one in ten having signed an online petition.
Smartphones and social media gave rise to "the Greta effect" where children are increasingly more active in matters of climate and social changes, inspired by 17-year-old Swedish activist Greta Thunberg.
Keeping children safe
Andy Burrows, head of child safety online at the NSPCC said, "While it's encouraging that parents are talking to their children about their media use, we must look to tech giants to protect their users and ensure they are a force for good not bad."