Background <p>Obesity and overweight in children contribute to developing kinematic gait deficiencies; however, reports on this matter are not conclusive. This study aims to compare the kinematics of the knee and ankle during walking between schoolchildren with overweight or obesity and schoolchildren with normal weight.</p> Methods <p>We conducted a cross-sectional study on schoolchildren aged 6 to 12 who were classified into three groups according to body mass index Z score: obesity ≥ 2.0 (<i>n</i> = 30), overweight 1.0 to 1.99 (<i>n</i> = 30), or normal weight − 1.99 to 0.99 (<i>n</i> = 35). The evaluation of the kinematics of the knee and ankles was performed through stereophotogrammetry, and the results obtained were compared between the study groups.</p> Results <p>We included 95 schoolchildren, primarily female (60%). We found no significant difference in flexion-extension movements between the study groups; however, we observed that the group with obesity presented a mean difference of 8.6° degrees (95% CI 1.55–15.65); <i>p</i> = 0.041 in right knee adduction during the initial swing compared to the group with normal weight and a mean difference of 6.35° (95% CI 0.26–12.94); <i>p</i> = 0.048 in the left knee also compared to the normal weight group. Additionally, we found differences in plantarflexion between the group with obesity and the normal weight group, with a mean difference of 6.41° (CI95% 2.61–10.22); p = 0.001 on the right side and the left side of 6.15° (CI95% 2.60–9.70); <i>p</i> = 0.003.</p> Conclusions <p>The kinematic differences in the knees and ankles between the obese and normal groups suggest “adaptations” during walking as their body weight increases.</p>