This paper examines the bilingual language development of young Korean–American children with respect to their acquisition of English grammatical morphemes and the different plural marking systems of Korean and English. We address two specific issues: (1) “do L1 and L2 learners acquire the grammatical features of a given language in the same sequence?” and (2) “do L2 learners of different L1 backgrounds learn the grammatical features of a given second language in the same sequence?” Comparison of our results with those of other morpheme acquisition studies suggests that L1 and L2 learners of English do not acquire English grammatical features in the same sequence. Furthermore, there is evidence that first language influences the course of second language acquisition. Results of an experimental study of plural marking suggest that the bilingual children in most, but not all, respects follow similar, but delayed patterns of first language acquisition of Korean and successive acquisition of English.