I don't know. I mean I certainly don't think he's an "abused" child. I know the family well (or thought I did!) and I'm sure it was a one-time thing, maybe dad was frustrated that he wouldn't sleep....I know he's not very patient with the kids from what mom has said previously, but under no circumstances do I think it's ok to punish in that way....
I think I do want to tell mom...like maybe say the child said it's ok to hit because daddy hit him....???? Bring it to her attention that way. I just don't know...