Objective of the study was to explore factors associated with early childhood obesity and assess whether having a foreign born mother is protective against childhood obesity. Data sources include 9 months and 4 years parent interviews and direct assessments of possessive children's weight and height (4 years) or length (9 months) from the Early Childhood Longitudinal Study-Birth Cohort. Subjects were children with anthropometric measures who lived with their mothers (n = 9,700 at 9 months and 8,200 at 4 years). Overweight is defined as a weight-for-length ratio at or above the 95th percentile at 9 months; obesity is defined as a body mass index at or above the 95th percentile at 4 years. The prevalence of overweight/obesity was 15.4% at 9 months and 18.0% at 4 years. After adjustment for potential confounders, having a foreign-born mother was not associated with the odds of overweight at 9 months or 4 years. At 9 months and 4 years, low birth weight, pre-pregnancy weight and weight gain during pregnancy were protective of overweight. In addition to these factors, at 4 years, excessive weight gain in the first 9 months was the strongest predictors for obesity. Living in a safe neighborhood and ever having breastfed were protective against obesity. Having a foreign born mother is not protective of early childhood obesity. A focus on health of women prior to conception and on women's and infants' health in the perinatal period are key to addressing childhood obesity.