Background: Income inequality is an important indicator of socioeconomic position which is a determinant of social, psychological, and physical health outcomes from childhood to adulthood. Different income inequality instruments (metrics) are used to investigate associations between income inequality and health outcomes (e.g. Gini coefficient). Income inequality instruments provide unique information on the construct of socioeconomic inequality. Albeit there is variation in studies as to the type and rationale for using a particular quantitative instrument of income inequality. The aim of this systematic review will be to investigate and identify the most used quantitative income inequality instrument in studies of children and adolescents up to 18 years of age. Methods: The PRISMA-P framework will be applied to identify high quality articles (PROSPERO: CRD42021259114). A search will be conducted in PubMed, Embase, and PsycINFO. The search will include studies concerned with income inequality and/or socioeconomic inequality in children and adolescents. All articles will be independently reviewed, data extracted, and quality appraised by two reviewers and a third to arbitrate disputes. Articles will be reviewed by title and abstract using inclusion criteria. A data extraction form will be used. Three questions will assess the quality of the rationale for using a particular income inequality instrument and the Newcastle-Ottawa Scale will be used to assess bias and quality. The primary outcome of interest is the type and frequency of quantitative income inequality instruments used and the study outcome associated with that income inequality instrument. Conclusions: This systematic review will aim to provide a summary of the different types of quantitative income inequality instruments used in studies of child and adolescent populations. This will help to guide researchers and policy makers on the use of income inequality metrics in future studies aimed at understanding associations with health and social outcomes in children and adolescents.