Looking for best approach for a remote user with children

My SIL and her 3 children use our server.

I'd like to do something that would prevent them from accessing files their mother doesn't appropriate.

There are a decent amount of files (movies) that appeal to all of the adults and kids.

There is a lot of tv shows they have too.

I've seen someone suggest setting a pin but not sure how annoying that would be to me since I use it far more often.

Also saw the suggestion of different libraries. I figure this is the way but I wanted to make sure I was doing it the ideal way.