M.I.
You sound like a very thoughtful parent, so i hope youll appreciate this info:
I have real concerns about the other child getting spanked for this .... This is how fetishes form. That is ... According to a terrific speaker in west 'burbs (mark mcdonald, psychologist) who spoke to our MOPS Lombard group (now disbanded, but you can find another chapter via MOPS.org) on the topic of "raising healthy children in an over-sexualized society" . Hesaid thatin situations like you mentioned, humiliating/shaming
punishment can actually create a sort of mental tape-loop reinforcing that same behavior when the intended result was DIScouragement of the behavior. He advocated a very calm, no-drama, no-shame approach. It's complicated & i am not a professionsal, so you (or the other parent) may want to read up on it or look up Mark McDonald (I think his practice was in Wheaton).