Best-selling author Dr. Andrew Weil believes anxiety and stress are some of the biggest reasons young students get sick at the start of the fall semester. "I think parents underestimate how stressful going back to school is," he says. "I think it's as stressful as a grown-up starting a new job."

Weil says stressed-out kids may complain of stomach pain or a headache instead of dealing with a stressful situation at school. He recommends training children to do simple deep-breathing techniques, just as adults do, to help with stress management.