I do think you can prevent it. I don't know that you can combat it but I do wonder if it is our various attempts to combat (i.e. go to war with) normal youth behaviour that has led to extremes like OP's.

From your link:

They spend the rest of their night at a special facility run by Mission Australia where they are fed and entertained until a responsible adult can be found to drop them home to.

I suppose its an improvement on the strip search my thirteen year old daughter received from the police who picked her up one friday after she wagged school for the first time ever and 'ran away from home'. A decade later, I'm still seething about the role these so called 'authorities' played in the whole situation.

I agree its all about perception. The Wests article ends with:

“But most often they are simply bored and come in to hang around with their friends and the city is the meeting point because all of the trains end up here.”

As a child we were often out at local parks without an adult for hours at a time. I rode myself to school from 6yo. It was normal. As a 15yo with an 18yo boyfriend, I was often out late on the weekends with the full permission of my very conservative parents. It was normal.

My question is: when did it become okay for the police to round up kids under 18 and send them home?

We've been 'increasing action' against youth for decades now. Is it possible it is this adversarial relationship that could have, in turn, led to depressing events like OP's? I fully agree, it is depressing to see kids behaving like this.

"You cannot force me to agree with you. You can only force me to act as though I agree with you - but then you'll have to watch your back. All the time." - L Neil Smith.