Yekke2:
Posek HaDor Rav Elyashiv zt’l paskened, and affirmed by the Moetzes Gedolei HaTorah, that one is prohibited to report to the authorities unless a competent Posek/Rov first rule the situation is raglayim l’davar. And the only exception he ruled is if the person actually witnessing the abuse himself/has first-hand certainty it’s occurring, that he may call the authorities without asking a shaila first.