On Last September, YouTube announced a series of changes that making to better protect kids and their privacy on YouTube, and to address the concerns raised by the U.S. Federal Trade Commission (FTC).
Specifically, that all creators would be required to designate their content as made for kids or not made for kids in YouTube Studio, and that personal information from anyone watching a video designated as made for kids would be treated as coming from a child, regardless of the age of the user.

Starting from 7th January 2020, will no longer serve personalized ads or support features such as comments, Stories, live chat, notification bell, and others on videos designated made for kids.

These changes may have significant impact on creators making kids content, so committed to helping them navigate this new landscape.

YouTube is continue to engage on this issue, including by participating in the FTC’s open comment period. Many creators have provided valuable feedback as well.
If you haven’t already, please ensure you have set your channel (or individual videos) as made for kids or not, as this will ultimately determine how your content is treated on YouTube.
Creators know their content best, and set the designation themselves. YouTube also use machine learning to help us identify this content, and creators can update a designation made by our systems if they believe it is incorrect.

For more visit https://youtube.googleblog.com/2019/09/an-update-on-kids.html?m=1