A number of studies in SLA and developmental psychology have shown that both children and adults can acquire nonnative word orders after a relatively short amount of exposure to a miniature language with natural-syntax characteristics in implicit instruction conditions. Although there is some evidence that in these conditions adult L2 learning can extend to morphemes (e.g., gender, case), little attention has been given to child-learning of morphology to date. In this pilot study six nine-year-olds and eight adults (all L1 English monolinguals) were exposed over three consecutive days to auditory sentence stimuli in BrocantoJ, a miniature language mirroring the word order and morphology of Japanese, in the context of a computer game similar to chess. Accuracy in performing a game move after hearing a sentence stimulus that described it, and accuracy in a forced-choice task, were used as measures of overall language comprehension and comprehension of the relationship between an argument’s syntactic realization and its thematic function (linking). The data showed that both groups performed significantly above chance overall and on linking rules. However, adults performed significantly better than children in the first two sessions (p < 0.01), though the gap disappeared by the third day. Also, initial evidence showed that, at least for a subset of the sentence stimuli, both children and adults were successfully relying exclusively on case marking to interpret NP thematic functions.