I know it gets frustrating when you have no help, but what you need to do is focus on the positive influence you bring to these children. I volunteer at the local library every Thursday, teaching the kids arts and crafts. The feeling of gratitude and admiration you get from the children after you help them learn something new more than pays for the time spent. If your problem comes from being overwhelmed and short-handed why not send out a notice that it is mandatory for one of each child's parents to assist with practice and transportation at least once a month? Include a schedule of events and your phone number. If they don't call you to pick their help date within a week, call them. It should effectively force the parents to take minimal interest in their kid's activities.