The purpose of this study was to investigate the differences in gait, pelvic movement, and medial gastrocnemius structure between typically developing children and children with delayed motor development with different muscle tone characteristics. Forty-five participants were divided into three groups: typically developing (TD) children (n = 18), children with spasticity (n = 17), children with central hypotonia (n = 10). BTS G-walk was used to measure gait and pelvic movement, and ultrasonography was used to measure medial gastrocnemius structure. In the result, children with spasticity had smaller peak angle of pelvic obliquity and pennation angle of medial gastrocnemius compared to TD children (p<.05), and larger peak angle of posterior tilt and rotation than children with central hypotonia (p<.05). Children with hypotonia had a shorter stride length and longer stance phase than children with TD (p<.05), and the thickness of the gastrocnemius muscle was thicker than children with spasticity (p<.05), but there was no difference in pelvic movement from TD children (p>.05). Therefore, it is necessary to recognize that the gait and muscle structure of children with delayed motor development are different depending on the muscle tone, and to propose an intervention program appropriate for their characteristics.