Dissociating the stem of verb forms is one of the main challenges facing the young children in first language acquisition. This study is concerned with the reconstruction of the stems in the natural speech of young children. Our analysis is based on the natural speech data collected longitudinally from 4 monolingual Korean-speaking subjects ages 2;06 to 3;06. Results show that (1) the children overall reconstruct irregular verbs more often than regular verbs, (2) the stem reconstruction takes place when the inflected form of a word contains an ellipsis or a contraction, (3) the children tend to substitute the variants which precede the universal ending `-아/어` morpheme. The implications of these findings are that young children consider the word forms that they are frequently exposed to as a basic form, and tend to change irregular paradigm to regular one. This provides evidence of the children`s capacity to dissociate inflectional features from a verb and to locate them in some other verb inflection.