[Brian]

First, make sure you've got version 1.9 of OmniFocus for Mac installed. ("Check for Updates" under the OmniFocus menu will grab it for you if you're running an earlier version of the app).

Once you've got version 1.9 (or later) installed, open the "Data" pane of OmniFocus' preferences, then check the "In Context Mode: Show Projects and Action Groups" box.

When actions are sorted by project, parent items follow their children (which is the natural order for completing them).

Single Action Lists are not actionable, and do not appear in Context lists.

Groups are also considered actionable. They can block other actions in a sequence, and are eligible to become the first "next action" for a project.

Projects and groups are blocked by their children, so if you're viewing Available actions in a context or due list they won't appear until all their children are complete...