Headteachers are warning parents that online 'suicide game' Momo is being spliced into YouTube videos of Peppa Pig and Fortnite.
Schools say children are being targeted by creepy images and clips of the disturbing character on the video sharing website.
The Momo challenge - which has been linked to two children's deaths - encourages youngsters to harm themselves and in some cases even take their own lives.
Today schools began issuing warnings on their websites and social media accounts saying they have been contacted by hundreds of concerned parents.
They said that the clips appear in the middle of seemingly innocent videos of children's cartoon Peppa Pig, or computer game Fortnite.
Haslingden Primary School, Rossendale, near Blackburn said in statement: 'We have become increasingly aware of highly inappropriate videos circulating online and are being viewed by children across the school.
'These video clips are appearing on many social media sites and YouTube (including Kids YouTube).
'One of the videos starts innocently, like the start of a Peppa Pig episode for example, but quickly turn into an altered version with violence and offensive language.