Video report by ITV News Consumer Editor Chris Choi
Children are not equipped for the digital world and are being left to "fend for themselves" against dangers such as bullying and grooming, the Children's Commissioner for England has claimed.
Children are spending hours online each week but parents are left "hoping bad things won't happen" because they feel they lack capabilities to deal with any issues, Anne Longfield said.
A year-long study into children and the internet, titled Growing Up Digital and published by the Commissioner on Thursday, claims that "much more needs to be done to create a supportive digital environment for children and young people".
Three to four-year-old children spend an of average 8 hours 18 minutes a week online - from watching films to playing games - while 12 to 15-year-olds use the internet for at least 20 hours per week, according to the report.
Ms Longfield has called on the government to take action and to teach children how to stay safe online.
The study found that children struggled to understand the "impenetrable" terms and conditions of social media sites and didn't realise what they were signing up to.
Ms Longfield has called on the Government to ensure that a search engine's "right to remove" facility - which applies to EU citizens - remains available to children in the UK after Brexit.
She has also urged the Government to appoint a children's digital ombudsman to act as a go-between for children and social media companies.
As part of the study, 900 Mumsnet users were asked about their worries with children using the internet.
It found that 73% of parents were concerned about their children accessing inappropriate material online and 54% were afraid of unwanted contact by strangers.
"Parents worry about what happens to their children online with regard to strangers and what children worry about online is what happens to them with regard to people they know or come into contact with - which is where bullying begins to really have an impact in terms of children's online presence," Ms Longfield explained.
The recommendations made in the report would give children and young adults the "resilience, information and power" they need to "open up the internet" without making them "vulnerable to having their personal information captured and monetised by companies", it states.
Barnardo's chief executive Javed Khan said: "This report provides further worrying evidence of how children are unprepared to deal with life online and receive little help in dealing with cyber-bullying, 'sexting' and harassment.
"Barnardo's welcomes the call to teach children aged four to 14 how to stay safe online, the dangers of 'sexting' and understand what they're agreeing to when using social media apps."
A Government spokesman said: "The internet has given children and young people fantastic opportunities, but protecting them from risks they might face online or on their phones is vital."
If you are in distress or need some support, the Samaritans are available 24 hours a day on 116 123 or visit their website.