Function words support many aspects of language acquisition. This study investigated whether toddlers understand the number feature of determiners and use it for noun comprehension. French offers an ideal “test case” as number is phonetically marked in determiners but not in nouns. Twenty French-learning 24-month-olds completed a split-screen experiment. Looking times to target pictures were measured under 3 trial types varying in the degree to which the determiner matched the number displayed in the object(s). Children looked longer when the determiner matched the object(s), and were confused in trials of clear mismatch. Importantly, their processing resembled that of French adults (D. Dahan, D. Swingley, M. K. Tanenhaus, & J. S. Magnuson, 2000). Thus, children understand the determiner number feature early in acquisition and use this knowledge to constrain online comprehension.