A Norfolk parent is encouraging others to ask their children about the Momo challenge after discovering his seven-year-old son had been exposed to it.

The 'game', which instructs young people to harm themselves and shows them graphic content, is most commonly associated with WhatsApp but has also been spliced into videos on YouTube and its sister site YouTube Kids.

Jamie England found out his son Harry had seen the 'scary woman', the female doll-like avatar associated with Momo, while watching videos on YouTube – but only after asking him about it.

'When we asked them my daughter said she hadn't seen anything but my son said he had seen it. I don't think he engaged with it but he knew what it was. He had problems getting to sleep that night,' said Mr England.

'But he had not said a thing to us until we asked him. I think it's best for parents to have the conversation with their children to find out if they have seen it.

'We were quite concerned about it. We reassured him that no one was going to come and get him, that it was someone playing a sick prank, but it is hard to explain that to a small child.'

Mr England, from Attleborough, was concerned about the number of parents who were dismissing the hype around Momo. He said: 'It is quite scary how many people are saying it is fake news and burying their head in the sand.'

Another mother from the Attleborough area, who wished to remain anonymous, felt Momo could have a 'petrifying' effect on younger children if they stumbled across the material.

'My four and a half-year-old daughter goes on YouTube on her iPad regularly,' she said.

'My husband and I discussed it [Momo] and we talked about changing the rules around how she uses YouTube.

'She is quite sensible and I think she would have told me if she had seen it. I've told her that if something comes up that she doesn't understand or someone tells her not to tell an adult about something, she has to come straight to mummy and daddy.'

The woman said she was now monitoring all of her daughter's internet use – and encouraging grandparents to do the same.

'Everyone relies on the internet but it shows you how unsafe it really is,' she said,

'It is ridiculous that we can't stop it and these little babies can see it.

'The worst bit was when people said it was on YouTube Kids. The whole point of that is that you are supposed to able to let your children go on it and not worry as it's so highly monitored.

'We have managed to escape it but I know a lot of kids have seen it and they are petrified.'