This study aimed to explore the teacher-parent cooperation with a special focus on language development at one multiethnic preschool in Sweden. Previous research has shown that the growing ethnical diversity in the society palaces high demands on the competence of educators to warrant high quality education for all children (Björk-Willén & Cromdal, 2009, Kultti 2012). Further, high quality ECE has been linked to well establish preschool-parent collaboration strategies, indicating that parent collaboration is a valuable resource in adopting a culturally relevant pedagogy (Tobin, Arzubiaga and Adir, 2013). The theoretical framework rests upon Bronfenbrenner’s bioecological systems model and the concepts of relational agency and boundary space as described by Edwards (2006, 2011). The project was conducted with an interactive case study approach, with field observations and interviews conducted with preschool staff at one multiethnic preschool unit. The study was conducted in accordance with the ethical guidelines of the Swedish Research Council, regarding informed consent, dissemination of results, and confidentiality. The study shows the importance of parent-collaboration in itself and concerning children's multilingual identity development. The informal parent-collaboration turned out to be most efficient compared to formal forms of collaboration. The teachers' beliefs about multilingualism being a "good thing" made the preschool unit work to highlight children's multilingualism and here parent-collaboration had a part. Knowledge about language development of dual language learnersand multiethnicity need to be more focused on both in teacher education programmes as well as in facilitating development of cultural awareness and competence in all educators.