Lyric discussion by conleyrasor 

Cover art for Uh-Oh lyrics by Fair to Midland

A kid has a fit and kills his girlfriend because she was crying. Him and his friend flee the scene visit the funeral and talk about what happened. What do I win?!

Another idea: serial killer. Kills children. Children familiar to serial killer. From the perspective of a bystander, perhaps a relative or close friend, hence the "I told you so".