As far as I know it only works with smartphones and tablets to limit children's usage, Android TV is still not supported but you can go to the help section of the app, find the send suggestions link and send a request, the more people send, the merrier.

I just tried to set it up to learn it's not available. Google means "wait for it...". And I'm so tired of waiting for Google to support all Android devices or all languages or all regions or....

It is in the Google Movies and TV app.