In a properly joined-up government effort, there would be coordinated action to fund and encourage youth clubs and youth activities with wide appeal - sports, music, drama clubs, science clubs, dance clubs, and so on.
The efforts of at least three government departments should be coordinated (Culture, Media and Sport, and Education, and Health) to promote a broad spectrum of youth activities, particularly in deprived areas that are plagued by anti-social behaviour. For a start, land could be provided for playing fields.
Where would the money come from? The Government would have to decide what kind of crusade it wants. Moral crusades may be waged with rhetoric only, but practical crusades need funding. In the long run, however, as the funding for youth activities rose, it might well be that the costs of vandalism, policing and prisons would fall.