Yes, curfews are an important tool in fighting juvenile crime. If juveniles have to be off the street, they can't be committing crimes. Not all parents keep a firm hand on their children, especially in the middle and high school years, and in neighborhoods where juveniles get into a lot of trouble, having a curfew in place increases public safety.
Yes, curfews are an effective way to reduce juvenile crime, because parents who set them are more likely to keep track of their children's activities. Involved parents, such as those who sets curfews, spends more time with their children. This allows the parents to have more influence of their children's lives, especially in teaching what actions are acceptable and unacceptable, and that there are consequences for unacceptable actions.
The U.S. Department of Justice compiled statistics over the course of the past 30 years that demonstrate curfews do appear to aid in reducing the level of juvenile crime. Additionally, data maintained by the Department of Justice supports the proposition that curfews combined with wholesome activities for children further reduces the incidence of juvenile crime. Midnight basketball leagues for teenagers is an example of such programming.
Curfews deter juvenile crime by making youth accountable for where they are after a certain time in the evening. This also helps their parents keep better track of their whereabouts. Being under a microscope of parents and authorities gives teams less opportunity to engage in devious behavior that leads to crime.