Increasingly, children with multilingual backgrounds are learning together in kindergartens. The study presented here illustrates the intricate interplay between multilingualism and mathematical learning through diagrammatic activity and communication about it in early mathematics education. The article introduces a learning environment developed for this purpose, which consists of elements in kindergarten and within the family. Observations of a boy in both settings show how he becomes diagrammatically active and communicates about it in both contexts. In particular, his interactions emphasize the value of integrating children’s linguistic diversity into learning processes.