IntroductionEarly childhood development (ECD) is a critical component for building the foundation of future physical and emotional health and subsequent academic success. The quality of the home environment to promote development is an important factor in ECD. Since large rural–urban disparities in the home environment exist in China, there is a critical need to develop and evaluate interventions to promote ECD in rural areas. Individual center-based or home-based interventions dominate the current ECD programmes in rural China. However, group-based interventions offer potential advantages in terms of both effectiveness and cost. Thus, we aim to: (1) evaluate the effectiveness of an integrated group-based intervention, the Care Group Intervention, in enhancing ECD among children age 6–18 months and (2) conduct a cost-effectiveness analysis.Methods and analysisThe Care Group Intervention uses a cluster (by township) randomised controlled trial conducted in Fenxi county, Shanxi province, China, from July 2019, for 1 year. The intervention focuses on five key components of nurturing care including good health, adequate nutrition, responsive caregiving, security and safety, and opportunities for early learning. The intervention comprises small groups of 3–10 children within a certain age range and their primary caregivers that are led by well-trained local facilitators. Outcomes includes infants’ developmental quotient (Bayley Scales of Infant Development III, Ages & Stages Questionnaire: Social–Emotional, second edition); anaemia (HemoCue Hb 301+); nurturing environment (Infant/Toddler Home Observation for Measurement of the Environment), parent-child interaction (Teaching Scale) and caregiver depression (Center for Epidemiological Studies Depression). Cost data are collected throughout the entire study to carry out a cost-effectiveness analysis.Ethics and disseminationThis study was approved by the Ethical Committee of Capital Institute of Pediatrics, Beijing, China on 10 July 2018 (SHERLL2018014). Findings and results from this project will be disseminated via publications and presentations.Trial registration numberChinese Clinical Trials Registry: ChiCTR1900022894. Registered on 30 April 2019.