A well-written protocol for pediatric randomized controlled trials is important to assess objective, design, implementation, measurement, planned analyses, and participant burden and safety. SPIRIT-C 2026 expands on the SPIRIT 2025 standard protocol items and the SPIRITcent-Childes statement, containing 17 core reporting items for pediatric RCT protocols. It was developed concurrently with the CONSORT-C 2026 statement for reporting pediatric RCTs. The document provides an explanation and elaboration with a pedagogical procedure for the development of protocols. It serves to create complex, transparent and high-quality pediatric RCT protocols. It is useful for trial candidates, funders, ethics boards, registries, regulators, systematic reviewers and journal editors. It concerns interventions in newborns, infants, children and adolescents.