This study investigated the developmental aspects of child EFL learners’ acquisition of grammar in an uninstructed setting where learning was based on input comprehension for the most part. Data were collected for two years from two Korean children’s written journals and compositions. The characteristics of their interim grammar were described with a focus on their awareness of syntactic constraints and production of functional morphemes. The study found that there were several peculiar features in their interlanguage such as excessive use of be as a topic marker, strong preference for regular morphology, and arbitrary conversion, and significant delays in the development of functional morphemes as compared to English L1 children. These suggest that in the environment devoid of pushed output and interactive pressure, input comprehension alone cannot lead child EFL learners to attain a fully operative state of grammatical competence.