Although many children become literate within an environment in which different language systems exist, there is still little research on what children know about different writing systems and how they understand and develop them when they are learning more than one alongside each other. Based on sociocultural theory and the concept of emergent literacy, which assume children as active language users in social processes, this research explores how Korean preschool children aged six make use of literacy knowledge and skills, and how they understand two different scripts, the Korean alphabet Hangul and the Roman alphabet used for English, in a foreign language context. 10 Korean EFL preschool children took part in peer teaching sessions, in 5 pairs, with each pair having a tutor child, aged 6, and a pupil, aged, 5. The tutor children taught literacy in both Hangul and English to the tutee children, and they led each teaching session in their own ways as active participants by using their own materials brought from their classrooms or homes as a teaching resource. The tutor children’s communicative interactions around reading and writing, written explanations presented on the paper, their behaviours, comments and responses during the peer teaching were observed and analyzed focusing on the meaning of what each child said, acted and wrote. The findings showed that the children were able to use their literacy knowledge and skills whilst engaged in literacy activities, and those knowledge and skills were shown in both two languages, at different levels: context, texts, sentences, words, syllables, morphemes, and sounds-letters. The findings also showed that they were able not only to find out key orthographic principles which characterise each writing system but also to seek the similarities and differences between two languages from different points of views: shape of letters (block shaped vs. linear), language units (syllables vs. letters), and sound-letter relationship (shallow orthography vs. deep orthography). The findings of this study suggest that young children are able to look for key concepts from different scripts from an early age, with the use of their literacy knowledge and skills in each script as active language learners.