The ubiquity of energy-dense and nutrient-poor discretionary foods in the current food environment, coupled with high exposure to child-oriented marketing, have led to excessive intakes of such foods (1). Dietary guidelines generally recommend consuming discretionary foods only occasionally and in small amounts (2, 3); appropriate portion sizes for children (that is, the appropriate amount to be consumed per eating occasion) are often not clearly specified, leading to confusion among caregivers and the public (4, 5). Hence, the aim of this scoping review was to map existing literature on discretionary food portion size guidance for children. The PRISMA-ScR guideline for scoping reviews was followed. Searches included four academic databases, grey literature, and hand searching. Eligible articles were those published between 2000-2025, included children and adolescents aged between one to 18 years, and reported data on guidance for portion sizes of discretionary foods. Studies were summarised by food type (such as biscuits, cakes, confectionery, ice cream, and soft drinks) and age group (pre-school, primary school, secondary school). Twelve articles on portion size guidance were identified. Most guides were sourced from websites of relevant health and professional organisations or government bodies (n=9), and three from peer-reviewed literature. The majority of articles originated from the United Kingdom (n=7), included pre-school children (n=7), and/or targeted education settings such as childcare providers and primary and secondary schools (n=6). Three records on parental guidance for young children were identified, and no guidance was found for parents of school-aged children. The primary sources of evidence were national dietary guidelines or dietary reference values aimed at meeting children’s energy and nutrient requirements, with portion size guidance typically presented as upper limits and accompanied by suggestions to limit consumption frequency (for instance, one portion of confectionery per week). Across food categories, portion size guidance (in grams) increased by 1.5- to 2.5-fold from pre-school to primary school age, and 2- to 4-fold from pre-school to secondary school age. These findings indicate that existing portion size guidance for discretionary food is designed to align with a balanced diet for children. Given most guidance originated from the UK and little guidance was available for parents, further context- and age-specific recommendations are warranted to support appropriate portion size selection. Strategies beyond guidance alone are required, for example, positive changes to the broader food environment that reduce the availability and promotion of discretionary foods in large sizes to support behaviour change and reduce intake among children.