White matter development continues into early adulthood, but specific regional trajectories in early childhood remain unclear. We aimed to characterize developmental trajectories and sex differences of white matter in healthy young children. 391 diffusion tensor imaging datasets from 118 children (59 male; 2-7.5 years) were analyzed using tractography. Fractional anisotropy increased and mean diffusivity decreased by 5-15% over the 5.5-year period, likely reflecting increases in myelination and axonal packing. Faster and greater development was observed in males during this period. The preschool period appears to be a critical period for the occipital and limbic connections, which underwent the largest changes.