The title of this thread is regarding child abuse.
A question asked in the OP is "Let us just take the cases where a regular publisher or even an appointed person, with no previous accusation of child abuse has come up against that person. Why do you feel that Watchtower is responsible for that person's actions against the child?"
In response, the WT would not be responsible for that person's actions. However, once the matter is reveled to Elders, even if not mandated by human law, there is a moral obligation to ensure the matter is reported to authorities, so an investigation may occur and the appropriate actions are applied.
If the incident report stops with the elders or with WT, then they are each assuming liability for further abuses by that person, whether to the same child, other children within that and other congregations, or children in the world. By ensuring the allegation is reported, then it can be demonstrated that appropriate and reasonable actions were taken by the elders/congregation. If Child Protective Services or other appropriate agencies do not proceed to investigate, then the liability for non-action is on them.
No mention of young persons who are deemed as having reached the lawful age of consent (ie: 14 in Austria), was made until RO's 4th posting.
If a person has attained the lawful age of consent and has consented to a sexual relationship with someone older, that would then not be illegal or considered a child abuse situation. I am not aware of any child abuse actions against WT, where this is/was the situation.