Some data or content gets rating info via their agents if not you can manually specify the rating or you can also use the “Label” value to allow access, so label an item as “Kids” and Kids have access to it just like ratings but less dynamic.
If you limit a users access they only see the items you restricted them to so Kids will not even be able to even see the Movie items rated above PG-13, they will only see the content they are allowed to view.
You can fast switch between users so you can switch from “Kids” to Main user with correct PIN very quickly to gain access to content other users may not have access to.
One other nice feature is if you setup trailers and have them setup to play before a movie if you play a movie rated PG-13 it will only play trailers for upcoming movies rated PG-13 and below so when you start “Cars 3” it will not play “Happy Death Day” trailer and scare your kid!
*** The only exception to this parental control at this time is the “News” feature where every device gets the full “News” feed but it is my understanding that ways of limiting managed users news sources is being looked into i.e. only Sports and Weather news items or something along those lines or possibly disabling News for specific managed users.