Childhood overweight is rapidly on the rise and underlies the younger presentation of diabetes. The aim of this study was to determine the association between overweight and age, sex, and the perception of the overweight children by their mothers. Three hundred and twenty-one (160 males) children (mean age 4.39 ± SD 0.83 yr) [body mass index (BMI) 16.6 ± 2.11] from schools at the kindergarten level were evaluated. Data on age, sex, weight, and height were recorded. At risk for overweight and overweight were defined as a BMI of ≥85th or ≥95th percentile, respectively. Written questionnaires for mothers' perceptions about their children's eating habits (a lot, right, little, or very little) and shape (very fat, fat, normal, and thin) were performed. The prevalence of at risk of overweight and overweight was 19 and 18.4%, respectively. There was a significant difference in the proportion of distorted perception of shape between mothers of normal-weight children vs. those of at risk of overweight and overweight children (17 vs. 87.5%, p < 0.001). Seventy-six and 98% of mothers of overweight and at risk of overweight children, respectively, rated them as normal or thin. Mothers exhibited poor overall ability to estimate the way at risk of overweight and overweight children ate. There was a significant difference in the proportion of distorted perception of eating habits between mothers of normal-weight children vs. those of at risk of overweight and overweight children (36.3 vs. 90.8%, p < 0.001). Eighty-four and 96% of mothers of obese and overweight children, respectively, thought that their children ate right or little. A multiple regression analysis using BMI > 95th percentile as the dependent variable showed that the mothers' perceptions of shape and eating habits [odds ratio 4.5; 95% confidence interval (CI) 2.5–7.8; p < 0.0001] were both significant independent risk factors for overweight, adjusted for age and sex. The agreement between the perception of shape and eating habits vs. the medical records BMI > 95th percentile was poor; for shape: kappa 0.31 + 0.07; 95% CI 0.17–0.44, and for nutrition: 0.14 + 0.06; 95% CI 0.02–0.27. This suggests that the mothers' perceptions of shape and eating behavior is a predictor of obesity and could be used in clinical practice as a simple tool to identify children at high risk for overweight.