Warning: This article is about suicide and may be distressing for some readers.
Parents in the United Kingdom and United States are being warned their children are being targeted after online "suicide game" Momo is to have appeared in YouTube Kids videos.
They said that the clips appear in the middle of seemingly innocent videos of children's cartoon Peppa Pig, or computer game Fortnite.
The "Momo" character - a scary doll's face - interrupts the show and threatens the viewer into contacting a number on WhatsApp.
In some cases the video says the children will be "killed in their sleep" if they do not contact "Momo".
Once the child has connected, the shadowy figures behind the "Momo" account can send what they like to the child on WhatsApp.
The Momo challenge has linked in news reports to the deaths of teens and children in a number of countries.
However, authorities in those cases have not confirmed the game to to be the cause of death.
Police believe hackers are using the "attention-grabbing" game to obtain social media users' personal information.
This week, schools in the UK sent out warnings on their websites and social media accounts saying they have been contacted by hundreds of concerned parents.
Haslingden Primary School in Lancashire warned of children's videos being spliced, The Mirror reported.
"We have become increasingly aware of highly inappropriate videos circulating online and are being viewed by children across the school," the school's Facebook post
"These video clips are appearing on many social media sites and YouTube (including Kids YouTube).
A statement from a YouTube says it has yet to find evidence of the Momo Challenge on its platform:
"After much review, we've seen no recent evidence of videos promoting the Momo Challenge on YouTube. Videos encouraging harmful and dangerous challenges are clearly against our policies, the Momo challenge included. Despite press reports of this challenge surfacing, we haven't had any recent links flagged or shared with us from YouTube that violate our Community Guidelines," the Google-owner service said.
"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.
"Another video clip is going by the name of 'MoMo' which shows a warped white mask which is promoting children to do dangerous tasks without telling their parents.
"Examples we have noticed in school include asking the children to turn the gas on or to find and take tablets.
"As you can imagine, this is highly distressing for the children to view. We encourage you to be vigilant when your child is using any device or watching any clips."
Daily Mail reported that Northolt Community Special School in Hull, East Yorkshire said: "We are aware that some nasty challenges (Momo challenge) are hacking into children's programmes.
"Challenges appear midway through Kids YouTube, Fortnite, Peppa Pig to avoid detection by adults.
"Please be vigilant with your child using IT, images are very disturbing."
Cleve House school in Bristol sent a letter to parents warning them about the online craze.
It said: "Light-hearted and fun at the outset, this game experience quickly darkens, absorbing players who are encouraged to perform acts of violence and self-harm through a series of progressively risky tasks. It is rapidly spreading across the world.
"The challenges issued in this game present a serious risk to the safety, welfare and wellbeing of young people in our school and in the UK."
A hair salon in the UK posted images on a parenting page of a 5-year-old girl who had cut her own hair, reportedly after watching a Momo video.
The hair salon urged parents and carers to be more vigilant online.
The post, from Toddler Trims in Gloucestershire said: "So I've just had a beautiful little girl in affected by this sick MOMO challenge!! If you are unaware this sick human/mutant is hacking into peppa pig, fortnight, minecraft etc..
"Any & most children's YouTube videos, telling them to cut there hair off, hold Knives up to there throat, set themselves on fire & that it will suck all the blood from there body ... this little girl is off to the doctors after her new haircut.
"She is five years old & still keeps talking about momo, her mother is absolutely devastated!!'
In the US, Brittany Roussell, of New Orleans, Louisiana, shared a video of her 6-year-old talking about seeing the Momo footage to raise awareness about the disturbing challenge, the Daily Mail reported.
She said she felt "sick to her stomach" when Bre-Andria told her about Momo's surprise visit in a video available on YouTube Kids.
"My daughter turned it off because when [Momo] shows her whole body she is naked and her breasts show," Roussell said.
Roussell has since deleted the YouTube app from her daughter's tablet to prevent her from being targeted again.
"She's a very good child and listens so I don't believe I will have the issue with her watching it behind my back," she said.
Roussell offered advice to other parents, saying: "Ask your children about Momo, show the pictures and talk openly with them.
"Let them know she is not real, and harming yourself or anybody else will hurt and it's bad."
What is the Momo 'suicide' game?
The Momo challenge was first reported in July last year, and was described as a new 'Blue Whale' style suicide game.
It started on WhatsApp, and challenged users to contact 'Momo' by sending messages to an unknown number.
The user was then hounded with frightening images and violent messages.
No one knows exactly where Momo originated, or who is behind the disturbing trend, though it was linked to at least seven phone numbers beginning with codes from Japan and multiple countries across Latin America.
The Momo challenge then started popping up in videos that were posted to social media.
The Momo avatar was created by Japanese special effects company Link Factory and designed by Midori Hayashi who has no relation whatsoever to the game.
The scary design originally featured at Tokyo's horror art Vanilla Gallery under the name Mother Bird.
Momo's features include a painfully gaunt face, bulging eyes and an unnaturally thin and long smile.
- source: Daily Mail
WHERE TO GET HELP:
If you are worried about your or someone else's mental health, the best place to get help is your GP or local mental health provider. However, if you or someone else is in danger or endangering others, call police immediately on 111.
OR IF YOU NEED TO TALK TO SOMEONE ELSE:
• 0800 543 354 (0800 LIFELINE) or free text 4357 (HELP) (available 24/7)
• YOUTHLINE: 0800 376 633
• NEED TO TALK? Free call or text 1737 (available 24/7)
• KIDSLINE: 0800 543 754 (available 24/7)
• WHATSUP: 0800 942 8787 (1pm to 11pm)
• DEPRESSION HELPLINE: 0800 111 757 or TEXT 4202