How could I help to prevent an eating disorder in my child?

Dont stress perfect. Children who develop eating disorders such as anorexia, binging and bulemia often show increases in these behaviors with stress and anxiety. High parental expectations and pressures and focus on external appearance and weight should be avoided. Obesity often results from lack of good nutrition, exercise or lack of attention to mood/hunger states. Good family support and balanced lifestyle help.
Calm consideration. Many factors are in play here. De-emphasizing body stereotypes, teaching eating for nutrition not for compliance or satisfaction, de-emphasizing meal compliance, encouraging a healthy self image, avoidance of using eating as a measure of being "good." encouraging exercise and physical activity. Avoidance of deprecating commentary about one's appearance. All will impact healthy self image.