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<div><p>Many autistic children have feeding problems, typically eating a limited range of foods. Feeding problems affect quality of life, health, and development. Research suggests that parents are often unsure when to or whether to seek help. When they do, local provision of help across the UK is often lacking. A toolkit could offer a tailored, accessible, and scalable early intervention to support parents. We aim to develop the blueprint of a toolkit to help parents/caregivers manage feeding problems in their autistic children. Medical Research Council guidance on developing complex interventions informs three successive work packages:\n</p><p></p><p></p><p>Realist review: a literature search and analysis using realist theory of logic to construct programme theory(s) in line with RAMESES (Realist And Meta-narrative Evidence Syntheses: Evolving Standards) guidance.</p><p></p><p></p><p>Realist evaluation: interviews of three groups: autistic children, young people and adults (<i>experts</i>), parents/caregivers of autistic children (<i>parents</i>), and professionals who help parents manage feeding problems (<i>professionals</i>) across the UK. Analysis of verbatim interview transcripts using realist theory of logic to refine programme theory(s).</p><p></p><p></p><p>Co-design of the toolkit blueprint: behaviour change theory applied to the programme theory(s) will generate candidate components for the online tool. A blueprint (a detailed textual outline) will be co-designed.</p><p></p><p></p><p></p><p>A participatory research team of <i>experts</i>, <i>parents</i>, and <i>professionals</i> will be involved in each work package. Where consensus is needed it will be reached by asynchronous nominal group technique. A PPI (public and patient involvement) advisory group of <i>experts</i> and <i>parents</i> will ensure the project is relevant, respectful, and accessible. Findings of each step will be disseminated via journal publications, conferences, social media, as well as PPI-co-produced webinars and a dissemination event. On completion, this project will provide the foundation for the subsequent development and refinement of the prototype toolkit.</p></div>