This presentation will discuss recent advances in our understanding of how motor commands are expressed across early stages of human development. In neonates, alternating spinal motor output reflects a simpler organization of neuronal locomotor networks. Basic motor modules are present at birth but are progressively reconfigured through continuous interactions among the brain, body, and environment. The complexity of motor modularity increases from the neonatal period to adulthood at multiple hierarchical levels of the motor system, from the intrinsic rhythmicity of individual muscle activity to the structure of muscle synergies and bilateral intermuscular connectivity. Particular attention will be given to mechanisms underlying impaired locomotor development, with a focus on spinal cord function. The first two years of life represent a critical window for the maturation of locomotor circuits. The emergence of independent walking during this period offers a unique opportunity to assess how neural circuitry develops in children with cerebral palsy. Recent findings indicate that achieving independent walking requires differentiation of proximal and distal extensor activity and an increase in the number of neuromuscular modules under corticospinal influence. While low complexity and high variability of neuromuscular signals reflect neonatal immaturity, they may also provide an adaptive substrate for learning locomotor skills.