This study examined Japanese-speaking mothers' passives in the child-directed speech from the CHILDES database. We selected five parent-child corpora and analyzed the overall distribution of the mothers' passives and further investigated the contribution of the construction and the passivized verbs to sentence meaning. The findings were as follows: (1) There are only a few verbs that accounted for much of the mothers' passives; (2) mothers' passives can be categorized into broad classes based on the verb-patient relation; and (3) most of the passives, both direct and indirect, were used to denote adversative meaning and these negative passives collocated with the verbal auxiliary "-shimau." We suggest that analyses of child-directed speech should take into account lexical repetition and the semantic redundancy of language as part of a process designed to support language development. Furthermore, highly frequent exemplar passives and their discrete reference in the events and contexts may be facilitative for children's learning of Japanese passives. The results are evaluated in light of the usage-based proposal of learning.