The age of consent in many areas is under 18 (I think Hawaii is as low as 14). That means it is legal for them to consent to activity with an adult (over 18). Should they too be permitted to “trade snapshots”?
Here it isn’t the taking the picture that is the crime. It is the distribution.
It is producing and distributing pornographic material to others, no consent involved. Those boys in turn probably distributed this material to others, and so one and so on. Just wait, I'll bet even more adolescent boys will be charged as those already charged talk.
How about this scenario: a couple gets married, with the wife being under 18. They take pics of themselves on their honeymoon engaging in activity that is, by virtue of them being married, perfectly legal in all 50 states. They can be charged with child pornography.