The Momo "Suicide Game" is one of the most disturbing games I've ever heard of. After reading up on it I'm not sure how or why it became a thing, but it is. It's been around for awhile now but has recently resurfaced.
The game can be played on WhatsApp, FaceBook, YouTube, and other online platforms. It encourages players, mostly kids, to slowly isolate and hurt themselves. The game has been linked to several incidents across the world, including the deaths of a 13-year-old Belgium boy and a 12-year-old Argentinian girl. In Edinburgh, an 8-year-old was told to get a knife from the kitchen and put it to his neck. In France, a father filed a complaint with the State Department after his son killed himself.
If you have a child, check with them and make sure that they're not playing this game. Go through whatever devices they have and double check. Even monitor the videos they watch because the challenges are appearing midway through Kids YouTube videos like Fortnight and Peppa Pig to avoid detection by adults.