The aim of the presented study was to assess changes in body composition and intersexual differences among children at pre-pubertal and early-pubertal age. The research was designed as a non-randomized cross-section study. The screened sample consisted of 136 girls and 212 boys assigned into three groups according to their age. Body composition was measured using a direct segmental multi-frequency bioelectrical impedance analysis (DSM-BIA). To examine the association between obesity and selected health-related parameters, Kruskal-Wallis ANOVA and Eta2 were used. For evaluation of intersexual differences, Mann-Whitney U-test was used. The presented article is the part of VEGA 1/0840/17 project. From the perspective of age, neither in the group of girls nor boys we recorded any differences in indicators of body composition, namely in body fat mass index, body fat percentage and, in addition, in the group of girls in the waist to hip ratio parameter.