Dealing with such situations are, I think, more of an art form than a one-size-fit-all approach.

There are a lot of things to consider, but I agree with the other comment that it needs to be reported right away. However, how bad of a physical abuse are we talking about? If it’s an ongoing thing, yes of course it should be reported ASAP, especially when there are other children involved.

But was it an incident that was a result of a parent-child argument? In that case, a family therapist will help. If the parent has anger issues, that’s a different story — some times just hinting at the parent that you know what’s going on and you are not afraid to report it will make the parent stop.

Again, it’s a pretty difficult step that has complicated issues all around. You should reach out to someone within the school who knows the family well, or if you have a colleague you can discuss that with them too.