Don't try to control them, try to make a difference in their lives. Try talking to the parents in person, with the students present. Ideally you would have both parents of each student in the conference. When you begin talking, be sure to start with something positive about the student. The parents might be on the defensive.
Every child has at least one positive trait.
Do this in front of the student and the student's parents. This might be the reason they act up in Sunday School. Talk to some of the parents of children you know should be in the class. Ask them why their children don't come. Tell them that you'd love to have their children in the class.