I love this. I wouldn't worry too much because kids' songs and old fairy tales are full of dark and disturbing images - London Bridge, Ring Around the Rosy, Little Red Riding Hood, the original Little Mermaid and Little Match Girl and all those Brothers Grimm stories. 3 Billy Goats Gruff is seriously disturbing. I get the desire to avoid talking to kids about things that are too heavy, but in that 7-11 age they are primarily fascinated by the battle between good and evil.
I remember being a kid, and my dad started playing Eric Clapton Cocaine. About halfway through he noticed I was singing along and clearly knew all the words, so he stopped and said, please don't sing that song in front of your mom.