It is estimated around one child in every primary school class in Britain has received an indecent image from an adult online, according to a recent survey.
An NSPCC poll of more than 40,000 children aged between seven and 16 also found that one in fifty had sent such an image to an adult.
The charity says that the rise of social media has played a big part and social networks have become “a gateway to child abuse”.
Campaigners say that because tech companies are not enforcing age restrictions, young children are now accustomed to being contacted by strangers online.
A ten-year-old girl explained how she had been harassed by a particular stranger who asked her to take her clothes off and send him a picture.
She said: “When I deleted the game, I went on another site and the same person asked me to have sex with him.
“I told him to ‘back off’ and then deleted that game. I have seen this person on many sites that I play and I decided to block him.”
In secondary schools, the problem is even more prevalent, with one in 20 aged twelve to 16 saying they had received at least one nude or semi-nude image from an adult.
A boy aged 15 said that the problem is not limited to strangers, saying: “My [sports] coach sent me a video of Santa stripping naked.”
Another explained that sexting was becoming normalised. A 13-year-old said: “A girl from my primary [was] sending half-naked pictures because it’s what everyone does.”
NSPCC Chief Executive Peter Wanless said that while parents and schools had a responsibility to teach children about how to stay safe online, “online platforms should be built to be safe in the first place”.
He said that poorly designed social networks and messaging apps “recklessly expose children to content and behaviours completely inappropriate for their age” and facilitate the sending of indecent images.
He concluded that all forms of social media need to be properly regulated “for the sake of children today and for generations to come”.