I can tell you from experience, nip this before it happens again. You need to decide if "nipping" includes momma or not, it really isn't fair or right to her to not tell her though, you can help temper her though.
The kid stepped over the line, make it so he wont do it again, because he will if you dont.
The kid stepped over the line, make it so he wont do it again, because he will if you dont.