content-featured-post.php

My original problem was how this theme uses same size images for full size “Featured Image” on “single post” as the thumbnails on featured content “Grid”. This results in getting an F for “serve scaled images” on nearly every page speed test on the Internet.

The fix was very simple: changing line 17 in content-featured-post.php from:
the_post_thumbnail();
to:
the_post_thumbnail(‘medium’);

Ok, so I created a child theme, then copied content-featured-post.php to this new theme directory, enqueued CSS as recommended, and then activated it. My version of the content-featured-post.php was completely ignored, and the theme parent theme version was used instead. Am I missing a step here?