My reception aged child has been playing "Huggy Wuggy" on the playground with friends, and is now scared to sleep by himself.
Apparently this character kills people by hugging them; it was originally in a 12+ game but it's now in Roblox games and YouTube videos, as well as in other types of games you wouldn't expect.
My ds has never played these games, but he's been exposed to it via adverts for games, as well as descriptions from friends.
I've spoken to his school today, and the teachers weren't fully aware of how scary it is and how many kids are playing it (my yr3 DD plays it with her friends too, apparently, though isn't as frightened).
This article from last month explains it better than I could - it's pretty twisted. news.sky.com/story/parents-and-schools-concerned-about-viral-huggy-wuggy-youtube-videos-12579453
(free, age appropriate games for kids seem to have these adverts, but unfortunately I can't control what he sees at his dad's house)