Questionnaires documenting children’s bilingual experience have been used frequently in research on language and cognitive development. However, there has been little investigation of the comparability between these tools. In this review, we (i) provide a list of available questionnaires used to quantify bilingual experience in children; (ii) identify the components of bilingual experience documented across questionnaires; and (iii) discuss the comparability of the measures used to operationalise these components. In doing so, we review 48 questionnaires and identify 32 overarching constructs, manifested as 194 components, and we calculate the frequency with which they are documented. Finally, by focusing on a subset of overarching constructs (language exposure and use, activities, and current language skills), we observe high variability in their operalisations across the tools. These findings highlight the need for greater transparency in how we document bilingualism and for more comparable measures.