I agree with you on the 'not letting them just continue on the streets'. I agree with you that something needs to be done. Where I disagree is with the idea of "adult crime, adult time". We essentially need to be running rehab centres, particularly for kids who are young. They don't need to go to prison, they need to be in centres where they can still access education, support services, socialise, engage in things in the way they would need to at that age. Even adults locked up need access to education, support services and rehab.
Whilst doing that, fix things at the root cause. The systemic issues such as cost of living, access to housing -negative gearing, access to education, access to support services, medicare, mental health services, and the current pricing out younger generations of just about any basic right.