Japan has seen a rise in the numbers of multicultural youth, both foreign-born and locally-born to immigrant parents, who navigate multiple languages across home, school, and peer relationships. Code-switching practices shape identity and affect cognition and psychological well-being, and schools, where children spend the most hours, pose unique challenges. Language barriers affecting peer relationships or academic performance can lead to significant psychological consequences such as social isolation and diminished self-efficacy. This study explores an after-school program for Chinese-heritage children that uses translanguaging to support plurilingual abilities, combining their Japanese learning with emotional support. Drawing on field notes and instructor interviews, this study examines both the implementation of translanguaging approaches and the psychological impacts on children. The findings demonstrate that the instructor established a more accessible plurilingual environment, while naturally guiding children to acquire Japanese expressions within authentic contexts through translanguaging practices. In this linguistically unconstrained setting, the children exhibited enhanced communicative motivation and more proactive learning engagement. Using their mother tongue as a resource, children transferred knowledge and met challenges otherwise difficult in Japanese-only contexts. This study provides empirical evidence supporting the pedagogical efficacy and research significance of translanguaging in facilitating children’s L2 acquisition and fostering their psychological well-being.