>As an anecdote I have close family member that teaches younger elementary school grades. They have told me about signs of possible abuse they've seen but no available recourse.
It's natural to want to stay out of things, especially if one doesn't know the procedure and worries about messing up a family's lives. But it's better for the people in charge of investigating cops abuse to decide the appropriate course.
As for how reporting happens, it depends on the state. In mine (Pennsylvania), all school employees are made well aware they're considered "Mandated Reporters." They are legally required to report any suspicions of child abuse, either through the state's website, phone line, local police, or the county agency responsible for child abuse cases. The suspected abuse victim doesn't need to say they're being abused or anything at all, the reporter doesn't even have to guess who the abuser is. If the reporter thinks there may have been abuse because they saw or learned about physical (e.g. bruises) or behavioral (e.g. afraid to go home) signs, they have to report it. Not reporting can led to misdemeanor or felony charges for the Mandated Reporter. Somebody who reported their suspicion is immune from civil or criminal liability, and protected from retaliation from the institution they work at, for the report (unless it can be shown they're using reports maliciously). They're also tested as confidential informants in any investigation.
The law also encourages "Permissive Reporters" to report suspected child abuse, but without threatening charges for not reporting. These reporters can do so anonymously.
All this info comes from my wife, who was a daycare teacher, and DuckDuckGo-ing "Pennsylvania mandated reporters."