This gives a few clear examples, but does not help much with slightly less clear judgements (e.g. should Nick Bostrom be a child of People or just tagged with it?). Classification systems are tricky and often subjective, probably worth taking a close look at Wikidata and other similar projects for inspiration when we want to work out detailed guidelines for this.
Comments
Alexei Andreev
Child, because "Nick Bostrom is a person" and "Nick is a part of the 'people' object" and without "Nick Bostrom" the object "people" is not complete.
You'd add the tag "People" if the page talks about that concept, eg a page about people of New York.
Eric Bruylant
If applied to all "is a" statements, some pages are going to have a lot of parents eventually. This is probably fine, but worth coming back to and reconsidering once we've seen the system in widespread use imo.