"Telltale" and "tattle" were the most intriguing connections. What is the impulse to "tell on" the sibling about? Obviously an effort at understanding something about rules and consequences, as well as an exploration of the variations of truth in a recounting. But it's the breaking of a co-equal bond with a or friend sibling, by invoking the authority of an older other, that makes the cultural denigration of the snitch make sense.
So the "Teacher's Pet" syndrome also enters here somewhere, I think, but I'm not going there right now. The upshot of the reflection is that questions are the key, and learning how to facilitate asking the right questions is the core of this work.