YouTube is filled with "kids" videos that frequently have a disturbing element to them. If you browse the platform you'll come across content targeted at children that has sexual or violent aspects. Those videos sometimes amass hundreds of thousands of views, presumably from very young users.
Now that these disturbing videos are being highlighted in outlets like The New York Times, YouTube is more significantly cracking down. When flagged, the videos will be age restricted and they'll be entirely disallowed from YouTube Kids.
Typically this content exploits kids-friendly characters like Spider-Man to attract viewers. YouTube first added a policy of demonetization for videos making "inappropriate use of family friendly characters" in August.
Along with waiting on reports from users, YouTube will have a team of humans working to identify and restrict these videos.