Drawing on international pedagogical discourse on the inclusion of ethnically diverse refugee groups in the educational systems of OECD countries as well as our previous research on the Ukrainian refugee perspectives on primary school in Switzerland, the author examines experiences of second language acquisition by displaced Ukrainian children in Swiss primary schools. The two-year research period allowed for the exploration of dynamics of German language acquisition by displaced children in conditions of full immersion in the target language environment and identification of the factors influencing their second language (German) learning and performance. The involvement of a Ukrainian researcher in the research project ensured accessibility of the target group and effective researcher-respondent communication in the course of longitudinal study carried out within the framework of a qualitative methodology with data collection through narrative inquiry and participant observations as research tools. The study identifies the effects of the two groups of factors: learner-internal (motivation, metacognitive skills, prior knowledge, and learning strategies) and learner-external ones (second language learning context, type of second language instruction available upon displacement, etc.). Metacognitive skills proved to be instrumental in second language learning in the context of the learners’ unexpected transition to a new educational setting and full immersion in the target language environment. Effects of metacognitive skills on second language learning of the studied group of displaced children vary considerably depending on the student’s age, prior knowledge and language learning experiences, and second language instruction available upon the displacement. The multidisciplinary character of the second language acquisition research undertaken by the author allows for diverse practical applications of its results in second language pedagogy, psychology of education, as well as in refugee and primary education.