One reason could be getting involved in theft. Juveniles might steal things like expensive clothes or gadgets either because they want to fit in with a certain group or because they come from a poor family and think stealing is the only way. Another reason is drug - related crimes. They could be selling or using drugs. Also, getting into fights and seriously injuring someone can lead to imprisonment for a juvenile.
There was a juvenile kid, let's call him Jack. Jack lived in a difficult family situation where there was little parental supervision. He started using drugs at a young age and in order to get money for drugs, he got involved in selling drugs too. Eventually, he was arrested and sent to prison for juveniles. In prison, he was scared at first. But over time, he started to realize the importance of making better choices with the help of the prison staff who provided him with education and support.
It could be a tale of a young person making a serious mistake and facing the consequences in prison. Maybe they got involved in something they shouldn't have due to bad influences or poor choices.