IntroductionOral language skills are associated with children’s later self-regulation and academic skills; in turn, self-regulation in early childhood predicts successful functioning later in life. The primary objective of this study is to evaluate the separate and combined effectiveness of an oral language intervention (Enhancing Rich Conversations, ENRICH) and a self-regulation intervention (Enhancing Neurocognitive Growth with the Aid of Games and Exercise, ENGAGE) with early childhood teachers and parents for children’s oral language, self-regulation and academic functioning.Methods and analysisThe Kia Tīmata Pai (Best Start) study is a cluster randomised controlled trial with teachers and children in approximately 140 early childhood centres in New Zealand. Centres are randomly assigned to receive either oral language intervention only (ENRICH), self-regulation intervention only (ENGAGE), both interventions (ENRICH+ENGAGE) or an active control condition. Teachers’ and parents’ practices and children’s oral language and self-regulation development are assessed at baseline at age 1.5 years and approximately every 9 months to age 5, and academic performance at age 6. Teacher–child interactions will also be videotaped each year in a subset of the centres. Children’s brain and behaviour development and parent–child interactions will be assessed every 6 months to age 6 years in a subgroup of volunteers.Ethics and disseminationThe Kia Tīmata Pai trial and the two substudies (Video Project; Brain and Behaviour Development) have been approved by the University of Otago Human Ethics Committee (Health; H20/116), and reviewed for cultural responsiveness by: the Ngāi Tahu Research Committee (University of Otago), the Māori Advisory Group (University of Auckland, Liggins Institute) and an internal cultural advisory group. Results will be disseminated in international and national peer-reviewed academic journals and communicated to local, national and international organisations serving early childhood teachers, parents and young children. Data will be available via communication with the corresponding author.Trial registration numberACTRN12621000845831.