Oh, fun! I get to advocate for the Devil.
Not, say, by having the police destroy the photos and telling them to go home and be smarter next time.
How much of a deterrent effect do you think this has? "OK, kids, you're creating a thing that is a complete abomination to the people of this state, a form of speech so vulgar that even the first amendment won't touch it, and that mere possession of it carries a prison sentence. And if you do it, you're going to get the worst talking-to you can imagine! We'll tell you that what you did was wrong! And that you shouldn't do it again! And we'll delete all the digital copies! Well, all the ones we can find, anyhow! That will teach you to manufacture child pornography! And you can bet we'll be devoting serious police and prosecutorial resources to ensure that we gently slap you on the wrist!"
It has to be the least intrusive means of furthering the state's compelling interest. Giving kids a lecture and telling them "don't do it again" does not effectively further those interests. The legislature has determined it should be criminal, and it's not in the power of the courts to say, "Well, it's a second degree felony, but screw the voters, we think it should be a fourth degree felony!" The state has a compelling interest, and any reasonable action short of criminalization will not effectively further that interest. It's not the place of the courts to be fine-tuning criminal punishments because they think the ones the legislature came up with are too easy (or too harsh).
As far as the summary of her talking to the cops, that's pure conjecture. We don't even know if she was interrogated; they certainly didn't need to talk to her once they had that evidence. For all we know, they found about the pictures because she called them out of fear her boyfriend would distribute them. I also doubt that the police were sophisticated enough to be prying into her grounds for a constitutional defense at the appellate level. And such an interrogation certainly isn't mentioned in the dissenting opinion (which is right below the majority one). And it's somewhat irrelevant; if she genuinely believed her boyfriend had a realistic chance of distributing them, she did not have a reasonable expectation of privacy. And if she didn't think there was any such realistic chance, she shouldn't have told the cops she was actually worried he'd distribute them.
This is a law governing the existence of a thing so abhorrent, mere possession of it is a felony. The state has a compelling interest, not merely in punishing those who create it, but in ensuring that it is never created in the first place. You may take issue with this, and say, "Well, it ain't so bad," but that's simply not what the law says, and you don't get to rewrite the law.
I'm not going to argue with the devil :-)
Merely to reiterate that the law on child porn doesn't care what the age of the creator (photographer) or the possessor is. It only cares what the age of the photographed minor is, for the purposes of defining child porn. But the two teenagers were found guilty in part because they were teenagers. If they had been adults, in possession of the same child porn (photos made of themselves years ago at age 16), then privacy protections would have applied. And so this is a small part of the relevance of this whole story to the original discussion on youth rights.
People debate all the time about how strictly children should be disciplined. Obviously, this is a worthwhile debate to have, as there must be some optimal amount of discipline that is greater than zero. The debate's nominal focus is usually on what's best for the child, with even the advocates for greater strictness arguing that it's "for their own good." It might also touch on what's good for other family members or for society at large. What I think is missing from the usual debate is that it assumes nothing but honorable motives on the part of the arguers. That is, it assumes that the arguments in favor of greater strictness are completely untainted by any element of authoritarianism or cruelty. But people are sometimes authoritarian and cruel! Just for fun! And the only people who you can be consistently cruel to without them slugging you, shunning you, suing you, or calling the police on you are your children. This is a reason for more than the usual amount of skepticism of arguments that say that strict parenting is necessary. If there were no such thing as cruelty in the world, people would still argue about the optimal level of strictness, and sometimes the more strict position would be the correct one, and parents would chose the optimal level of strictness on the basis of these arguments. But what we actually have is a world with lots and lots of cruelty lurking just under the surface, which cannot help but show up in the form of pro-strictness arguments in parenting debates. This should cause us to place less weight on pro-strictness arguments than we otherwise would.* Note that this is basically the same idea as Bertrand Russell's argument against the idea of sin: its true function is to allow people to exercise their natural cruelty while at the same time maintaining their opinion of themselves as moral.
One example of authoritarianism masquerading as sound discipline (even among otherwise good parents) is the idea of "My House, My Rules." I've even heard parents go so far as to say things like: "it's not your room, it's the room in my house that I allow you to live in." This attitude makes little sense on its own terms, as it suggests that parents would have no legitimate authority over, say, a famous child actor whose earnings paid for the house. Worse, it's a relatively minor manifestation of the broader notion that the child has a fundamentally lower status in the family just for being a child, that they deserve less weight in the family's utility function. I don't think this is what parents would be saying if recreational authoritarianism really were not a factor. They would still say that they, by virtue of their superior experience and judgment, get to make the rules (i.e., decide how to go about maximizing the family's utility function, though even this might be done with more authoritarianism than is necessary). But you wouldn't be hearing this "I'm higher than you in the pecking order and don't you dare forget it" attitude that is so very common.
*Some might argue that arguments should be evaluated solely on their merit, and not on the motives with which they were offered. This is correct when the validity of the arguments can be finally determined. For most kinds of persuasive argumentation, especially in complicated and emotionally laden subjects like child rearing, arguments work on us without us ever being able to fully evaluate their merit. And in that world, it does make sense to down-weight arguments that have some bias built into them.