Wait a minute - how can we say some people are not adults in any way [voting, alcohol, sex, marriage] except legal culpability? There's a very good reason why they can't expect the rights of an adult: their development is incomplete, and they haven't gained the knowledge, experience, and maturity to make choices as an adult. But that doesn't matter when they commit a serious crime?
Why aren't they reevaluated at age 21, or 25, to determine whether they remain a threat to society?
As Tbub noted, sexual predators cannot presently be treated as cured, ever, but how many of the minors were cognizant of the nature of the acts committed as children? Maybe all of them, but it seems unlikely, really.[ Haven't we all seen little kids playing 'doctor', who hadn't the faintest idea of why it so horrified adults?]
It's quite possible that a reevaluation would find those convicted as children perpetually unfit for society - but shouldn't they be judged as adults, when they reach that age?