We examined French-learning toddlers' sensitivity to Subject-Verb agreement with conjoined subjects. In French, a conjoined NP triggers plural agreement even when made up of individual singular NPs. Processing of this infrequent structure in the input (see Corpus Analyses) requires going beyond surface patterns of non-adjacent dependencies to abstract, feature-based syntactic knowledge. In Experiment 1, results revealed a significant grammaticality effect in 24-month-olds, but not in 18-month-olds, with no interaction with the condition (with either conjoined or non-conjoined agreement; all tested with Head-Turn Preference Procedure). In Experiment 2, 30-month-olds (tested with conjoined agreement only) showed the same pattern as 24-month-olds: a strong grammaticality effect limited to the first half of the experiment. Overall, these results provide some support to the hypothesis that 24- and 30-month-olds (but not 18-month-olds) have abstract knowledge of SV agreement with conjoined subjects, although it imposes a high processing cost. Importantly, this abstract syntactic sensitivity precedes the earliest evidence of simple agreement comprehension.