Is there a way to get children documents using GET and not SEARCH?

Goal: Get all children documents given parent document ID as fast as possible.

If you know the Parent ID and use nested instead of Parent/child, you can achieve the above by using GET Api (
I was wondering if you can do something similar with Parent/child schema. It seems like Child has _parent field, but parent does not track list of all the indexed children?
I've only seen implementation using HasParent query, which is using Search, and not as fast as I'd like.
Since I have other use cases not supported by Nested structure, I want to use Parent/Child, is there a way to retrieve all the children documents that would give me faster time than using HasParent?