Paranormal Romance

I like the rhyme, but if these Molly Malones target rapists and murderers, would children have to worry about them? Maybe you could look taking at a slightly different angle, where the children have a rhyme they chant during skipping rope or another game. Something similiar to Oranges and Lemons, perhaps, particularly the ending.

I think as a rhyme for children it's got a good rhythm and bit of graphic horror to it that's reminiscent of the ghost stories we'd try to freak each other out with when I was young.

However, I don't know that 'break your heart' would be particularly creepy to a kid, and the verb is repeated in the same line, so I'd recommend a change to that bit (smash your heart? eat your heart?), but otherwise should suffice.