Childhood obesity is associated with many adverse health effects during childhood and is linked to an increased risk for obesity in adulthood. The objective of this study was to determine the characteristics of early childhood overweight and obesity and assess the impact of breastfeeding. Data from Hawai'i's Special Supplemental Nutrition Program for Women, Infants and Children (WIC) were analyzed for children 2 years of age born between 2005 and 2009 and their mothers. Childhood overweight and obesity was examined using a log-binomial regression model to estimate prevalence ratios. In the sample population, 12.5 % of children were overweight and 8.5 % of children were obese. Significant differences in childhood overweight and obesity were seen between breastfeeding duration and other socio-demographic groups. Children who were breastfed for 6 months or more had a lower risk of childhood obesity at age two compared to those who were never breastfed (APR 0.79, 95 % CI 0.69-0.91) with adjustment for child race/ethnicity, maternal age, trimester of prenatal care entry, maternal smoking status, and child birth weight. The prevalence of early childhood overweight and obesity is associated with shorter durations of breastfeeding. Early and continued breastfeeding support and education for mothers in the WIC program that improves duration of breastfeeding may help reduce the risk of early childhood obesity.