Prisoners have (at least, allegedly) committed a crime and deserve their time.
Children haven't committed a crime, yet must spend most of their waking life there.
And no, they cant just go home whenever they want, they have to be dismissed from their daily sentence and go home tired and weary after being indoctrinated for 7hrs in a prison environment, only to look forward to waking up and doing it all over again during the most energetic years of their life.