To be honest, that isn't a subject we've really covered in my program (which seems odd, since I know it's not terribly rare for children/teens to abuse other child/teens). Ultimately, I think it boils down to 1) the intent of the perpetrator, and 2) the resulting feelings of the victim. For example, two children may play "doctor," and if there isn't any intent to manipulate/control, or any feelings of being violated, I wouldn't rush to call it child-on-child sexual abuse. After all, children DO express curiosity about sexuality starting at a young age. Obviously, my answer would change if the perpetrator's intentions weren't innocent/ignorant, or if the victim felt dirty/ashamed/etc. afterward.