"not sure about abused but there has to be have been something to make them even think of it in the first place, let alone try it."

There have been incidents where children who have been involved in assaulting other children appear to be attempting to mimic behaviors that they have been forced to submit to by adults. One I can think of where a little boy made a little girl take his penis in her mouth in the school toilets, he then pee'd in her mouth. Not exactly oral sex because clearly it wasn't a *sexual* act for him, but that's what he was mimicking. From memory, the boy had been sexually abused himself.