I know there's a lot of parents here so thought I'd post this:
www.manchestereveningnews.co.uk
www.telegraph.co.uk
It was popular last year with Youtubers 'playing' it. Apparently a 12 year old girl committed suicide over it and another kid was told to hold a knife to his throat. Its horrifying.

Parents warned disturbing Momo challenge is 'hacking Peppa Pig' YouTube videos
Videos showing the creepy character popping up in seemingly innocent Peppa Pig episodes are being widely circulated on Facebook
YouTube and Instagram fail to take down 'Momo challenge' videos despite police warnings
YouTube and Instagram have failed to take down content featuring an online character targeted at children despite new warnings from the police.
It was popular last year with Youtubers 'playing' it. Apparently a 12 year old girl committed suicide over it and another kid was told to hold a knife to his throat. Its horrifying.