The present study investigated young children's external source monitoring abilities in identifying two source persons. In the acquisition phase, children listened to a set of target words read by two speakers (a male and a female) under two conditions (3 alternative condition in which the speaker read the target words only unique to each sources (he/she); 4 alternative condition in which the speaker read the target words that some target words were common to both sources, whereas others were unique to each source). Following the acquisition phase, participants were given a recognition test and a source monitoring test in which they identified the source of each target word by means of alternatives (i.e., 3 alternative condition: male voice only, female voice only, neither; 4 alternative condition: male voice only, female voice only, both, neither). Results showed that the children under 4 alternative condition made more source monitoring errors than did the children under 3 alternative condition. Thus, the young children had more difficulty in identifying source on the task including "both" judgment.