This study investigated the preattentive processing of abstract acoustic regularities in children aged 8-14 years. Event-related brain potentials (ERPs) were elicited by frequent (standard) pairs ascending in pitch (the second tone having a higher frequency than the first tone) and by infrequent (deviant) pairs descending in pitch. In the easy condition, the second tone of the pair was always one step higher (standard) or lower (deviant) than the first tone, while in the hard condition, the second tone was randomly 1-10 steps higher or lower than the first tone. In the easy condition we found the mismatch negativity (MMN) and a subsequent positive P3a-like deflection. In the hard condition, the amplitude of MMN was lower over frontal sites than in the easy condition, while the temporal component of MMN was not impaired by complexity of abstract regularities. These results suggest that the complexity of the auditory stimulation affects preattentive auditory change detection in children.