A SEVEN-YEAR-OLD girl started banging her head against the wall at school and refused to go to bed after being terrified by the sick Momo challenge.

Callie Astill was so scared she wouldn't even go to the bathroom by herself - plagued by nightmares from the freaky online character.

Momo, initially a Japanese sculpture, has been overtaken by sick Internet trolls using the image to terrify youngsters - reportedly popping up in YouTube videos and on Fortnite to issue challenges and threats.

The sick avatar has sparked warnings from schools and even police as the trend sweeps the UK and world.

And mum Victoria Turner said she was "devastated" when she asked her daughter about Momo after seeing online warnings - with the schoolgirl immediately screaming.

She said: "She had her fingers in her ears, burst into tears and it took a long time to console her. When she could speak she said ‘Mummy it’s a secret, I can’t tell you’."

Victoria, also mum to four-year-old Lola Russell, said that before she realised Momo was the cause of the upset she’d received calls from the school two weeks ago expressing concern about Callie’s change in behaviour.

The waitress mum-of-two said: "Prior to this I had the school ringing up saying that Callie was acting awfully strange.

"She’s quite a good girl but there was a distinct change in her behaviour, I did wonder whether she was being bullied.

"She was purposely banging her head on walls and asking to come home and wouldn’t go to bed.

"I thought ‘what’s going on here? This isn’t my Callie’. I thought I was doing something wrong or that it was a behavioural issue but now it all adds up - she was frightened to death."

Callie, who loves watching cartoons including Minecraft, is still frightened of the figure and refuses to be drawn on the details of what she saw.

A YouTube spokesman said they hadn't received any evidence of videos showing or promoting the Momo challenge on YouTube and that content of this kind would be in violation of their policies and removed immediately.

But Victoria said her children's only internet access was through YouTube Kids.

She said: “Whoever is behind it, they’re obviously not right in the head, people gets kicks out of the most disgusting things.”

Now UK schools up and down the country are warning parents to be on their guard as kids receive sick challenges to self-harm or death threats by the online character.

Police Service of Northern Ireland has even confirmed it is liaising with other UK forces over the 'disturbing game'.

Detective Sergeant Elaine McCormill said: "This extremely disturbing challenge conceals itself within other harmless looking games or videos played by children and when downloaded, it asks the user to communicate with 'Momo' via popular messaging applications such as WhatsApp.

"It is at this point that children are threatened that they will be cursed or their family will be hurt if they do not self-harm."

A YouTube spokesman said: "Contrary to press reports, we’ve not received any recent evidence of videos showing or promoting the Momo challenge on YouTube.

"Content of this kind would be in violation of our policies and removed immediately."

However the company confirmed they have seen content reporting on the Momo character and people have sent them screenshots of thumbnails with the Momo character in it, but said the content had been 'focused on discussing/documenting/reporting on the challenge and the character'.