See
http://en.wikipedia.org/wiki/Image:Teen_Shelter_in_Stockport.JPG
Teen shelters, a fairly recent idea. Local authorities put them in the
local park. Its a place for teens to congregate. Here they can smoke,
drink have sexual explorations,engage in anti social and criminal
behaviour and no one can see them.
Without a teen shelter, they would have to do all the above out on the
streets where someone would have to see them and someone would feel
obliged to do something about it i.e the Police. Out of site-out of
mind, unless of course you live near one.