Previous studies indicate that English-learning children acquire the distinction between singular and plural nouns between 22 and 24 months of age. Also, their use of the distinction is correlated with the capacity to distinguish nonlinguistically between singular and plural sets in a manual search paradigm (D. Barner, D. Thalwitz, J. Wood, S. Yang, & S. Carey, 2007). The authors used 3 experiments to explore the causal relation between these 2 capacities. Relative to English, Japanese and Mandarin had impoverished singular-plural marking. Using the manual search task, in Experiment 1 the authors found that by around 22 months of age, Japanese children also distinguished between singular and plural sets. Experiments 2 and 3 extended this finding to Mandarin-learning toddlers. Mandarin learners who were 20-24 months of age did not yet comprehend Mandarin singular-plural marking (i.e., "yige" vs. "yixie", or "-men"), yet they did distinguish between singular and plural sets in manual search. These experiments suggest that knowledge of singular-plural morphology is not necessary for deploying the nonlinguistic distinction between singular and plural sets. (Contains 2 footnotes and 4 figures.)