According to Ofcom data, over 25% of five- to seven-year-olds in the UK currently own a smartphone.
Despite WhatsApp's 13-year-old minimum age requirement, over two out of every five users in the age range used the messaging app last year.
The communications regulator cautioned that there "seemed to be diminishing" parental enforcement of standards.
It said that the numbers need to serve as a "wake-up call" for the sector to take further precautions against child abuse.
According to Ofcom's annual survey on kids' interactions with media and the internet, the proportion of kids between the ages of five and seven who use messaging services has increased from 59 percent to 65 percent.
The percentage climbed from 30% to 38% on social media and from 39% to 50% on livestreams. A little more than 40% are said to be playing video games online, up from 34% the previous year.
Contrary to the policies of most major platforms, more than half of children under the age of 13 accessed social media, and many of them acknowledged lying to get access to new applications and services.
According to BBC News, Mark Bunting of Ofcom's Online Safety Group says, "They have to take account of the users they have, not the users that their terms and conditions say they have." "I believe that the industry needs to wake up to this."
Protesters advocate for raising the current age limit for social media use and introducing new ones for smartphone use.
This article was originally published on the BBC.