Background: The purpose of the present study was to determine the impact of the direction and magnitude of primary lateral spinal curvature in children with scoliosis. Methods: Ninety-six children diagnosed with scoliosis were included in the study group, and fifty healthy peers were included in the control group. Posturographic measurements of body weight distribution and posturometric tests with eyes open and closed were performed. Results: Based on the symmetry index values, the study group was divided into children with symmetrical and asymmetrical body weight distributions on the basis of support. Then, taking into account the direction of the primary curvature, children with asymmetrical body weight distributions were divided into: (1) children with left-sided or right-sided scoliosis with overload on the same side of the body; and (2) children with left-sided or right-sided scoliosis with overload on the opposite side of the body. According to both posturometric tests, increased CoP spatial displacement was observed in the children with scoliosis compared to the healthy controls. The obtained results showed that increased asymmetry index and Cobb angle values significantly increase medial-lateral postural instability in children with scoliosis. Conclusions: These findings suggest that treatment to restore symmetric body weight distribution may prevent the progression of postural instability; however, this requires confirmation through further investigation.