The answer is already built into MacOS. It is called a "smart folder", which is a view of a directory based on a query. So you can query all files in your subdirectory recursively, with a "kind" restriction if you like.

How to create a Smart Folder
 - In the Finder on your Mac, choose File > New Smart Folder.
 - Specify the criteria. ...
 - Click Save. The system asks for a name and location for your Smart Folder.

There are excellent videos on the internet introducing smart folders. Check them out.