Early brain development may soon be measurable through sleep patterns rather than waiting for behavioral milestones to emerge. This precision could transform how pediatricians identify developmental delays in preverbal children, potentially enabling interventions months earlier than current methods allow. High-density EEG recordings captured distinct sleep brain wave changes in 11 healthy infants between 3 and 6 months of age. Slow wave activity increased most dramatically in the visual processing regions at the back of the brain, while theta frequencies showed widespread increases across all brain areas. Perhaps most intriguingly, sigma power waves initially clustered around central brain regions but gradually spread toward frontal areas responsible for executive functions. The strength of these frontal brain wave increases directly correlated with superior motor skills and social development scores at 6 months. This represents the first longitudinal evidence that sleep-based neurophysiology can predict individual developmental trajectories in infancy. The findings suggest that different frequency bands reflect distinct aspects of brain maturation, with theta waves linked to motor development and sigma waves associated with social skill acquisition. From a clinical perspective, this research addresses a critical gap in early neurodevelopmental assessment. Current developmental screening relies heavily on behavioral observations that may not detect subtle delays until well into the second year of life. Sleep EEG could potentially serve as an objective, non-invasive biomarker that identifies atypical development patterns months before behavioral symptoms become apparent, opening windows for earlier therapeutic intervention when neural plasticity is at its peak.