To get it back on topic:

Hello Eldorado Girl, from another Edinburgher!

Well, when I was little my favourite 'lullabies' were gory ballads. I have not to the best of my knowledge grown up an axe-murderer, sister-killer or evil stepmother. Sing your son what he likes, he's only four months. As he gets older he'll learn to distinguish right and wrong and suchlike, you seem pretty well-balanced so I'm sure he will be too.