Warning: This article has disturbing content and mentions childrens suicide.
In a Facebook posting Saturday titled "Suicide game targeting our kids", the Police Service of Northern Ireland cautioned parents that the game can hide "itself within other harmless looking games played by our kids!"
"Momo" started on Facebook and involves members who are challenged to communicate with an unknown member.
Concerns have been raised over children's online safety after rise of new MOMO game..
Using a character called Momo, the game encourages players to perform a series of risky tasks including disturbing acts of self-harm.
She also shared a message, seemingly sent to her by a friend, which read: "The Momo Challenge sent the other day is apparently now in kids' YouTube". CBS News did reach out to Link Factory for comment.
The Momo Challenge is an alleged form of cyberbullying which can be found on WhatsApp, a mobile phone messaging service.
The Momo Challenge is a disturbing "game" that reportedly entices social media and WhatsApp users to communicate with an unknown number that sends graphic images and orders them to carry out risky and even suicidal acts.
Now, certain children's YouTube videos are being hacked by Momo, with the creepy creature appearing midway through the clips to threaten the kids watching.
The police email added: 'Children are subsequently bombarded with terrifying images and messages reportedly ranging from threats and dares which encourage them to self-harm and even commit suicide'. "More important is that your child knows not to give out personal info to ANYONE they don't know, that no one has the right to tell them to, or make them do ANYTHING they don't want to", according to the post.
"It is a danger and it would be irresponsible for us to disregard it".
Roussell offered advice to other parents, saying: "Ask your children about Momo, show the pictures and talk openly with them. Challenges appear midway through Kids YouTube, Fortnight, Peppa pig to avoid detection by adults", the Northcott Community Special School in Hull, England, wrote on Twitter. "Please be vigilant with your child using IT, images are very disturbing".
Haslingden Primary School in Rossendale, near Blackburn, was among the institutions which put out warnings about Momo.
YouTube issued the following statement to CBS News regarding the challenge: "Our Community Guidelines prohibit harmful and risky challenges, including promoting the Momo challenge, and we remove this content quickly when flagged to us".
There have been numerous reports on social media of people from across Northern Ireland seeing the character pop up while their children played a game or watched a video. In December 2018, WhatsApp was criticized for failing to stop the spread of child porn in chat groups.