If you want to talk about the legality of Watchtower reporting cases of child porn then stick with the legality of it. If you want to speak about the morality then stick with that. Just because it is pointed out again it is a complex issue and a worldwide directive has to vary to some degree based on jurisdictions and how certain governments view it then you immediately switch. Is child porn showing the abuse of a child of course. but it is not that simple anymore.
There is a segment of porn that depicts legal performers that look exceptionally young in porn or the fantasy of some people to watch porn that fantasies legal performers who pretend that they are high school students. It is the law defines what is allowed depending on the jurisdictions. Then you have some countries where even the sex acts of not 18 year olds but only 21+ is allowed. It is a complex situation.