Semantic transparency is known to affect the rate and course of lexical acquisition, including the slow and gradual acquisition of Japanese numeral classifiers. There has not been, however, an effective definition as to what constitutes semantic transparency. In an effort to better understand the determining factors that affect the slow and gradual acquisition of Japanese numeral classifiers among young children, the current study examines comprehension of six Japanese numeral classifiers (-ri/-nin, -hiki, -dai, -hon, -mai, and −ko) among 90 monolingual speakers of Japanese ages 3, 4, and 5. In particular, this study attempts to explore semantic transparency with two types of classifiers, kind and shape. This study is also interested in young children's ability to generalize their knowledge about classifiers. The study employs a forced-choice comprehension task. The stimuli consist of familiar or unfamiliar real objects presented in a between-participants design. The results show that comprehension increases with age except comprehension of −ko. In this case, the comprehension level remains at around chance even among older children. The results further indicate that comprehension of kind classifiers is significantly better than that of shape classifiers. This effect is especially evident when applying classifiers to unfamiliar stimuli, suggesting that kind classifiers are not only easier to acquire, but also easier to generalize. Examination of semantic transparency offered by kind classifiers indicates the existence of consistent and reliable cues. These results suggest that semantic transparency that offers consistent and reliable cues has a major impact on the acquisition of numeral classifiers.