Query list of issues and all of their subordinate issues

[Jamie Edmondson]

I have a list of various issues in Jira that have been given to me. I can create a Filter like this:

issuekey in (ABC-123, XYZ-456, ALPHA-455, BRAVO-434)

This will return a list of all of those issues. By the way, in our custom hierarchy, the issues above are all "Features". Our hierarchy is Feature > Epic > Story > Task > Subtask

What I need is to return all of the issues that are the children, or "subordinate" issues in the hierarchy. I'm not sure how to make this happen. I've tried to use Scriptrunner as well and not having much luck. 

My goal is to have all of these created in Advanced Roadmaps; however, the only current way that I know how to make this happen is to add every project I am referencing and then remove any issues that do not apply to the plan -- one by one. Very painful.

Any ideas?