The children's commissioner for England is calling on internet giants and toy-makers to be more transparent about the data they are collecting on children.
Today's children are the first to be "datafied" from birth and little thought has been given to the consequences, a report for her says.
Who Knows What about Me? calls for a statutory duty of care between social media giants and their younger users.
And it urges the government to consider strengthening data protection laws.
'Canary in mine'
The report also highlights how very young children are now using toys that are connected to the internet.
These gather personal messages and information that may be insecure and open to attack from hackers, it says.
The report quotes research led by Sonia Livingstone, who describes children as the "canary in the coal mine for wider society" - the first to encounter new technology and its risks before many adults are even aware of them.
- children should be taught in schools about how their data is collected and for what purposes
- where a toy collects any video or audio generated by a child, this should be made explicit in a prominent part of the packaging or its accompanying information
- using language children understand, companies should explain clearly in their terms and conditions what data is collected and how it will be used
The report estimates:
- between the ages of 11 and 16, children post on social media 26 times a day, on average
- by the time they reach adulthood, they are likely to have posted 70,000 times
- by the age of 13, a child's parents will have posted on average 1,300 photos and videos of them to social media
There is also:
- the data gathered when children use the internet
- tracking devices and apps used by parents to keep tabs on their offspring
- the biometric data held by public bodies such as schools and the NHS
The report warns that there could be risks to young people where profiling of internet usage is utilised in areas of life where it can have deeper ramifications, such as the judicial system or the education system.
One worrying scenario it gives is if a health insurance company used information posted by a child on social media about their mental health as part of its decision on whether to issue a policy or how much to charge.
Anne Longfield, the Children's Commissioner for England, said: "We need to stop and think about what this means for children's lives now and how it may impact on their future lives as adults.
"We simply do not know what the consequences of all this information about our children will be.
"Companies that make apps, toys and other products used by children need to stop filling them with trackers and put their terms and conditions in language that children understand.
"And crucially the government needs to monitor the situation and refine data protection legislation if needed, so that children are genuinely protected - especially as technology develops."