The creation of it certainly remains illegal, and its existence is a violation of individuals right to privacy (these images are never taken with consent, because the victims cannot consent). In the same way you could consider it a violation of your privacy for someone you do not want there taking your picture in private, child porn violates the same principle.

So child porn can be perfectly illegal without having an explicit law saying "Child Porn is illegal". Its creation violates so many fundamentals and its distribution violates a subset of those.

But the reason for the illegality is as important as the legality in the first place. Some of the most horrible nations commit acts we deem moral in consequence but often do them for still vile reasons (ie, you don't execute the mafia boss for rampant murder and robbery, but because hes threatening your own power).