The regulator calls the data a "wake up call", and says parents and industry need to do more.
Nearly a quarter of UK five-to-seven-year-olds now have their own smartphone, Ofcom research suggests.
Social media use also rose in the age group over last year with nearly two in five using messaging service WhatsApp, despite its minimum age of 13.
The communications regulator warned parental enforcement of rules "appeared to be diminishing."
It also said the figures should be a "wake up call" for the industry to do more to protect children.
In its annual study of children's relationship with the media and online worlds, Ofcom said the percentage of children aged between five and seven who used messaging services had risen from 59% to 65%.
The number on social media went up from 30% to 38%, while for livestreams it increased from 39% to 50%. Just over 40% are reported to be gaming online - up from 34% the year before.
Over half of children under 13 used social media, contrary to most of the big platforms' rules, and many admitted to lying to gain access to new apps and services.
Is it bad for kids aged 5-7 to have smartphones? Is it worse than the pre-smartphone era when kids that age watched hours of TV instead?
It is absolutely worse. There are horrific things on the internet, and lots of fucked up ideas. Before smartphones there was cable, where you had 75 channels of often vapid but vetted content.
First of all, there were horrific things on TV news all the time before smartphones, and on cable TV which was not vetted because it is not overseen by anyone. The FCC has no power over it. That's why there are porn channels.
Secondly, you're talking about unrestricted internet access, not smartphone access. Those are entirely separate things. It is very easy to make a smartphone child safe.
Thinking even a simple majority of parents who give their 5 year olds smartphones are using any kind of parental control is a naive fantasy.
Separately, there were no 5 year olds watching the nightly news by themselves in their bedrooms, but regardless, scenes on TV news and TV as a whole are pale in comparison to what's available on the internet. Cable channels were absolutely vetted lmao...they were productions of large media conglomerates that had no interest in risking profits. Porn channels were rare, and required extra effort to access. We're not talking about 13 year olds staying up late to catch a boob on Cinemax
That wasn't criticizing them for not choosing to give their kid a phone, that was criticizing them for not choosing to give their kid a phone because it is a "mind sucking waste" as if that sort of language hasn't been used to describe TV and video games.