I suspect there isn't a word for a parent losing a child because it is a more common event than losing a spouse or both parents, and not a singular event. J. S. Bach had 20 children, only 9 survived past childhood. "Childless" could apply to someone who had lost all his/her children or to someone like me, who never had any.

Songs that stick in your mind: earworms or loopers. Some songs are deliberately composed to loop back, with a dominant chord at the end of the chorus that is only resolved by the first chord in the next verse, or repeat of the chorus. I'd mention some examples, but I wouldn't want to infect anyone.