TL;DR - Thousands of extremely unpleasant videos have been published to Youtube for Kids where they have got billions of views. In many cases the videos have expensive production methods such as stop motion. Youtube has been aware of the videos since 2015. Here is an informative video on the topic.

Just a heads up, there are disturbing content and themes here. This topic is not for the feint of heart.

https://www.youtube.com/watch?v=32X45J-MRUE