This article explores the development of the language alternation practices of a bilingual child who is growing up with two languages: English, which she speaks with her father and older brother, and Italian, which she speaks with her mother. It reports on a microanalysis of the dyadic interactions between parent and child when the child was aged 18-24 months. The analyses focus on how and when parent and child attend to language alternation as they interact with each other in everyday contexts such as mealtimes, shared book reading, and play. The results of this study frame simultaneous bilingualism as a matter of the local situated concerns of the participants that can nonetheless have a developmental focus. The data are in Australian English and Italian.