Childhood obesity has become a major societal concern. Rates of obesity among preschool and school-age children have more than doubled in the past three decades: 14% of 2- to 5-year-olds and 19% of 6- to 11-year olds are obese (Ogden et al. 2006; Ogden et al. 2002). The increased rates of obesity have become a public health concern because obesity is associated with chronic disease and adverse health outcomes (Institute of Medicine 2005).