The aim of this study was to determine the risk factors of childhood obesity among infants and toddlers from low-income families from three cities in Mexico. This is a cross-sectional study of mothers and their infants and toddlers attending a vaccination centre at three primary care clinics in Tijuana, Tuxtla, and Reynosa. Anthropometric measurements of the mothers and children were conducted at the clinic and a questionnaire was administered to the mother. Eight-hundred and ten mothers and their 5 to 24 months old infants participated in the study. Average age for the mothers was 24 (21-28) years, and 57% of them were either overweight or obese. The children's average age was 12.7 (5-24) months. Overall overweight prevalence in this sample was 11% and obesity 8%, these increased with age, from 3% for overweight and 6 % for obesity before 6 months, to 13 and 10% between 12 to 24 months respectively. Thirty-five percent of infants were breastfed>or=6 month and 92% were introduced to other solid foods before 6 months. Introduction of high-fat content snacks (HFS) and carbonated and non-carbonated sweetened (CSD) drinks starts before 6 months and more than sixty percent of the children between 12 to 24 months of age were eating HFS and CSD sweetened drinks at least once a week. Consumption of snacks and CSD sweetened drinks (>or=1 week) was associated with being overweight and obese (crude), OR, 1.82; 95% CI=1.24-2.65 (p=0.002). These results suggest that preventive programs should be initiated during pregnancy and continued.