Previous work on children’s acquisition of Japanese numeral classifiers has provided extensive information regarding classifier acquisition and its effect on cognitive development (e.g., Yamamoto, 2005). However, few studies have examined the considerable variability found in these studies. We propose that variability in children’s classifier acquisition may be due to input. Thus, we examined parent input of Japanese numeral classifiers to Japanese-speaking children. Participants were two- to five-year-old monolingual Japanese and bilingual Japanese-English children and their Japanese-speaking parents. Parents were instructed to “read” a wordless picture book about counting to their children. Book readings were video-recorded and coded for frequency, type, and correctness of parent classifier use. Children also participated in Give-N and counting tasks. We hypothesize that children whose input includes many generic classifiers (e.g., -ko: generic classifier for inanimate objects) will have more advanced number understanding than children whose input includes more specific classifiers (e.g., -ken: classifier for houses).