Numerous studies have shown that skeletal characteristics vary among different populations. Several authors suggest that it is possible to determine sex through the anatomical evaluation of children mandible, however there are few morphometrical studies conducted with such specimens. The purpose of this study was to analyze several mandibular dimensions and identify the ones that could be useful to perform sex differentiation in a sample of Brazilian young children. For this study we used 32 children dry mandibles of known sex, age ranging from 0 to 1 year old. The mandibles pertain to the collection of the Skull Museum of the Universidade Federal de Sao Paulo (UNIFESP). The parameters included bicondilar width, bigonial width, minimum width and height of the mandibular ramus, gonion-gnation length, height of the mandibular symphysis and transverse and anteroposterior condylar dimensions. The SPSS program was used to carry on the discriminant function analysis and the T test (p <0.05). There were no statistically significant differences that could allow identification of a specific parameter for sex determination. However, most of the dimensions were higher in male than in female, except for the minimum width of the mandibular ramus (0.2-0.16 mm) and transverse diameter of the right condyle (0.16mm). The values obtained for the anteroposterior diameter of the mandibular head were the most different between genders, although no statistically significance was found. Discriminant function analysis indicated that, despite differences, none of the evaluated parameters allow for sex classification with enough reliability. In conclusion, there is little sexual dimorphism in children's mandibles during the first year of life and anatomical analysis of this structure is not recommended as reliable quantitative approach for sex differentiation with forensic purposes.