Obesity is a complex multi-factorial condition that results from genetic predisposition and lifestyle factors such as high energy food consumption and physical inactivity. The heritability of childhood BMI has been estimated to be 40-70%. The high heritability of obesity in the context of the current obesogenic environment strongly suggests that genetic factors are implicated in population patterns of obesity and, as we propose here, are essential to consider in population approaches to address the obesity epidemic. Identifying genetic factors that influence early childhood BMI can inform the etiology of obesity as well as help to identify strategies to prevent and treat childhood obesity and related adult cardiometabolic diseases. Currently, the genetic factors that influence early childhood BMI are not well understood. Genome-wide association studies (GWAS) could help identify these genetic factors and distinguish their effects across ages. The Collaborative Perinatal Project (CPP) was a prospective pregnancy cohort that enrolled women who had prenatal care at 12 medical centers in the United States from 1959-1965. Women were followed from early pregnancy onwards and their offspring were monitored from birth through 7 years of age. While the CPP enrolled children prior to the obesity epidemic and obesogenic lifestyle in the United States, any potential interactions between genetic factors discovered using this cohort and recent environmental modifiers can be validated using other more recent cohorts. The CPP offers opportunities to discover novel genetic loci related to obesity among Africans and Europeans and to improve the functional characterization of known loci discovered in European populations.