A Zoom hacker "horrified" a group of about 60 children taking part in a fitness class when he streamed child sex abuse footage, police have said.
The class was being hosted on Tuesday by a sports club in Plymouth when the youngsters were exposed to the "extremely distressing" material.
Devon and Cornwall police believe the hacker gained access after the call's details were published on online forums.
The hacker is yet to be identified.
Officers are collaborating with Plymouth city council's social care team to identify everyone who was exposed to the footage.
Det Insp Lesley Bulley said: "We are working closely with Plymouth Safeguarding Children's Partnership and I request that, if you have been affected by this, then you come forward and let us know who you are so we can provide the necessary advice and support."
'Lock it down'
The force issued advice to the public on how to ensure they are safe before accessing conference calls, including keeping details private and devices and software up to date.
People should also always only download from trusted sources such as the Apple App store and Google Play, while the conference host should ensure the call is locked once all guests have joined, police said.
"Keeping in touch with our friends and family is vital during this period of lockdown," cyber protection officer Grahame Mace said.
But he urged people to understand their device's security settings, adding: "Don't leave yourself or others vulnerable, lock it down and keep the criminals out."
Anyone affected by what happened, or who has information, is urged to email firstname.lastname@example.org or call 101 quoting crime reference CR/035950/20.
Any adult concerned about the welfare of a child or young person can call the NSPCC helpline for free and confidential advice on 0808 8005000 or visit nspcc.org.uk.