[Plugin: Yet Another Related Posts Plugin] YARPP thumbnails break on child themes?

I just activated my child theme (with no alterations to the files yet) and my YARPP thumbnail images stopped appearing. Once I reactivated my original theme they came back. Is there something I can alter in the YARPP code, or templates? I believe I’m just using the thumbnail template altered a tiny bit to not include the rating numbers.

My site on Personal Mythology