I, too, have zero tolerance for the parent who is "immune" to their screaming child. Rambuctious is one thing, screaming because momma won't do anything about it is another.
Saying anything to the other guy can be considered "escalation." Ignore him, and if he moves toward your family, get between him and them, warn him once that you're about to call 911 and have him arrested. If he makes a futher move, then I'll pay the cards as they fall.