How do I get the folders that are inside a Knowledge Center?

I have a rule.  That rule needs to get the child folders of a Knowledge Center.

If it were a folder, I could just use "folderChildren" property and I would be done.  But Knowledge Centers don't have a "folderChildren" property.  I don't know why they don't.  But they don't.  All Knowledge Centers DO is store folders, so it floors me that no one has had this problem before, but apparently no one has had this problem before.

How do I get the "folderChildren" but of a Knowlege Center?