The length of time spent in detention depends on the nature of the offense and the sentence handed down by a judge. Some juveniles may spend only a day or two in detention, while others could spend over a year in the facility. The average stay in a juvenile detention center is just under 30 days. This means that most juveniles spend less than a month in a detention facility. You should also remember that some juveniles get charged as adults - especially when they commit a felony or capital offense. This rarely happens on misdemeanor charges. When convicted as an adult, the juvenile will be moved from a juvenile detention center to an adult jail. In most cases, the child must be at least 16 to be charged as an adult, although the laws vary from state to state. However, even if the child is being charged as an adult, Federal law generally prohibits them from being housed in adult jail while awaiting trial.