Need to get all children from multiple parents

[joe weiss]

Here is my hierarchy

Story > Feature > Journey Epic > Product Epic

I have been able to get children from a collection of items in the past via issueFunction in linkedIssuesOf("project = CAT", "link that represents parent to child")

There are parent and child links available in my world but nothing that I enter in the 'description' above will get me the children that I want.  I've tried

• issueFunction in linkedIssuesOf("project = CAT", "is parent of")
• issueFunction in linkedIssuesOf("project = CAT", "is Epic of")
• issueFunction in linkedIssuesOf("project = CAT", "is Child of")

Nothing works.

Thoughts?