If a juvenile commits a crime, he or she should have to pay a price. But solitary confinement is too steep a price for a child. I can't imagine the emotional and mental toll of being alone all the time — if you ask me, it's torture. But you don't have to ask me.
The cynical way to look at this is to write them off as criminals who deserve to "just do their time." If you're inclined to think that way, consider this: Most prisoners return to society after their sentences are complete. What will make them more likely to be good citizens: solitary confinement or rehabilitation programs?