My liability is to report anything "suspicious" however....please keep in mind, kids "stories" can seem alarming sometimes, when in fact they are not. Maybe these parents "spank" and maybe he had been up many times through the night with verbal warnings going "un-aknowledged". In my area we are resposible to report abuse and neglect (not sure if this really is though) however, I also feel it is best to go to the parent first. Do you have any reason to feel this father could be abusive? or do you think he's just "old school", "hard,hard,hard" could just be because his Dad has never spanked him before and it seemed hard. either way, if their are no marks...I'd give some time and observation along with more convo's (loosely based) with this little boy. Don't forget, let him talk, don't talk for him. Never say things like "does Daddy Hit you" then you put the idea in his head, "oh , yes..daddy hits me" when he very well may not.
Some people do "spank" as punishment, and it's not considered abuse by some. By others it is.