More on KentOnline
School staff say they are "absolutely appalled" after pupils as young as 11 were groomed on social media.
One parent at Cedar Children's Academy, Cedar Road, Strood, warned others how her daughter was targeted by a man on Snapchat who had "exposed himself".
She explained how a safeguarding officer from the school told how one of her children was being targeted by a man online.
The mother said: "Today I had every mum's worst nightmare. To be told by my daughter's school that her and her friend had seen an indecent image.
"In my mind I thought 'okay, we all get some sort of spam in an email or accidentally find something', but this was a video on Snapchat.
"A sick man has been grooming her, making a group of 'Cedar School Friends', so they were both curious and added themselves in and the girls were chatting among themselves to find out he had been listening in."
The mum, who we've chosen not to name, explained how her 11-year-old began asking her sex-based questions.
"We are absolutely appalled by this incident, which underlines the dangers children can face on social media..."
She continued: "Next he sent them a horrendous video, where the dirty scum revealed himself in a video to my child and another innocent little girl.
"A lesson learned – talk to your children, search phones, regularly update privacy settings, talk openly about sex."
A school spokesman said: "As soon as we became aware of this, we immediately informed the pupils’ parents, the police and other relevant authorities, in line with our robust safeguarding procedures.
"We are now supporting the police with their inquiries and all parents have been made aware of this extremely concerning incident to ensure they are extra vigilant.
“The safety and wellbeing of all our pupils is our number one priority. We are absolutely appalled by this incident, which underlines the dangers children can face on social media, whether in school or at home.
"As an academy, we regularly hold sessions with all our pupils so they are aware of the risks and know how to stay safe online.”
New data released today by the Internet Watch Foundation (IWF), a charity which aims to reduce sexual abuse and child sex images, revealed more than three quarters of sexual selfies they found were from girls aged between 11 and 13.
It also claimed young girls are being "tricked" into performing sex acts online.
IWF chief executive Susie Hargreaves said: "Today’s data demonstrates the alarming rate at which self-generated imagery is increasing, especially among young girls – often in domestic settings.
"These are images and videos where girls have been groomed, coerced and tricked into performing sexually over webcam, what is fast becoming a national crisis."
Jo Pattison, spokesman for Kent Police said: "Kent Police received a report of suspicious activity on an internet app used by a number of children.
"The matter is under investigation.
"An appointment has been made for an officer to speak to those concerned and safeguarding information has been provided."