Filter for sub-tasks by Parent Key

Ability to filter for sub-tasks of a particular parent key number.

ie
abc-001 Parent Issue
->abc004 Sub-task 1
->abc005 Sub-task 2
->abc006 Sub-task 3
->abc007 Sub-task 4

Filter for Sub-task 1,2,3,4 by searching for abc-001

My team currently has only JIRA project available so we create our teams "projects" by creating a parent issue as the project and the sub-tasks are the issues relating to that parent issue/project. We need to have a way to search for the sub-tasks for a particular parent issue.