What can we do about the neighborhood kids who leave garbage at our front door?

My family and I live in a duplex apartment building where there are about 17 apartments, the kids come out to play in the courtyard and leave gum wrappers, paper and at one point left chewed gum on the floor and I had to sc it up. These kids age range from 5 to 14. I don't want any problems with the parents. I had a problem with one parent who didn't like it when I knocked on his door to tell him that his son had thrown mud at my door.