This study examines how young immigrant children in multilingual playful activities with peers and adults engage with and explore heritage language forms (e.g., their features, social values and pragmatic uses), as well as transgress boundaries between different language varieties. It is argued that such ludic language practices – located and enacted within micro-interactional processes – in turn link to and contribute to macro-level socio-cultural values and tensions of languages. The selected data constitute a case study based on a video-ethnography of multilingual language practices in a preschool (for 3- to 6-year-olds) with a Swedish monolingual policy. It is found that the children's multilingual play involve the exploitation of heritage language and linguistic incongruities: it takes the shape of exaggerated repetitions, transformations of language forms (phonetic, morphological and syntactic features), various keying resources, i.e., affective (serious or ludic) and metalinguistic stances. The findings underscore the importance of taking into account young immigrant children's agency in creating new spaces (e.g., ludic or instructional activities) for heritage language forms and varieties as they are used for entertaining, rather than educational purposes.