<sec><title>Aims:</title> This study investigates whether, to what extent, and in which direction interface structure induces cross-linguistic influence (CLI) in the use of objects in Japanese/English simultaneous bilinguals.

</sec><sec><title>Design:</title> Year-long observations of parent–child interactions in two two-year-olds were conducted to observe the changes taking place at the earliest stages of development.

</sec><sec><title>Data analysis:</title> A total of 48 recording sessions were transcribed and coded using Computational Human Articulatory Theory conventions and were compared with mean length of utterance-matched monolingual data drawn from the CHILDES database.

</sec><sec><title>Findings:</title> We report a temporary influence from Japanese to English and a mild influence from English to Japanese.

</sec><sec><title>Originality:</title> This study offers evidence of CLI in object use in less-studied language pairs.

</sec><sec><title>Implications:</title> The data support the interface hypothesis and further suggest that the language combination affects the intensity of influence due to the degree of the overlap. Our data also add evidence to the proposal that without language dominance, CLI occurs from the overt language to the language with null options.

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