The whole purpose of child pornography laws is to protect the minor victim.
Under the law, a minor child CAN NEVER give consent to a sexual act. Period. There are exceptions for teenagers with other teenagers, but beyond that there is no exception (hence statutory rape laws). The whole point of making child pornography possession illegal is to get around the loophole of "I have a picture of an illegal act, but you can't prosecute me because you do not know who is in the picture."
Now when you actually KNOW who was depicted in the picture, and the circumstances surrounding the picture, you can make a determination as to whether the underlying sexual offense has taken place.
I find it impossible to comprehend the charging of a minor for possession of THEIR OWN PORNOGRAPHY!!! We are now prosecuting the person whom the law was written to PROTECT!!!
The question should not be "is it pornography?" The real question is "was the person who is shown in the photograph illegally exploited?" That is a much simpler question to come to terms with, and by ignoring that question, you make a mockery of the legal system.