During child development, physiological changes occur in the auditory cortex, which are reflected by differences in the electrophysiological signals. This study aimed to examine the age-related changes of the Mismatch Negativity component (MMN) in response to speech and non-speech stimuli in a cross-sectional design. Results revealed distinct patterns of activation according to stimulus type and age. Age-related differences for tone discrimination occurred earlier in children's development than did the discriminative process for speech sounds. Therefore, networks involved in speech processing are still immature in late childhood and may be more vulnerable to physiological changes.