I think this will be on a long list of things like this which are reported daily to police and social services and schools.
They should act on it but it could take a while.
Sex between 2 x 13 year olds is not unusual. Nor is them filming it and sharing it. There are lots of questions that need answered about context- Were they both consenting? Do they both know it is being shared? Was anyone else present? Was there coercion? Are either of these children already known to social services and regarded as vulnerable? Is there evidence of previous similar behaviour? Is she pregnant?
I think parents generally, would be horrified if they knew what, and the amount of what, schools/police/social services deal with on a daily basis.
It is a complex issue with many facets for each agency.
I dealt with something similar as a Deputy Head 10 years ago, with two 16 year olds and a video of them having sex which they had shared and was being blu-toothed around a group Y11 boys in their friendship group. Called the police, informed local authority safeguarding lead. Police came in, scared them, made the whole group wipe their phones, warned them about what they were doing. (But it would still be out there somewhere). Took names and addresses. Took the two involved in the video home, spoke to their parents. Parents shocked. There were no other concerns for social services. It was an established relationship. No coercion- and they just showed it around. Obviously, they were over the age of consent but it was 10 years ago and less common then. It is much more common now.
I think it needs a multi-agency approach to look at the circumstances of and protecting the two involved, but if it's out there I can't see what they can do to stop it now. Teenagers watch porn. If they watch it, the rest follows. It's a society issue. As usual, no one took any notice of the people who said it was a bad idea to make phones/computergames/internet/ porn/vapes/alcohol/drugs so common and accessible.
How many people here access it? Play violent computer games? Send sexts? And possibly daily. It's part of millions of lives. It's part of teenagers lives. Impossible to police.