AbstractBackgroundUnhealthy lifestyle behaviours such as a poor diet, inadequate physical activity, and excessive screen time have been shown to be established in childhood and track into adulthood, demonstrating the need for health promotion interventions in the pre-school years. The overall aim of this project is to: (i) evaluate the effectiveness of `Saga Stories in health talks´ within child healthcare (CHC) on parental self-efficacy to promote healthy diet, physical activity, and screen time behaviours in their child; children’s intake of key dietary indicators and screen time and (ii) evaluate and explore the implementation of `Saga Stories in health talks´ with regards to acceptability, appropriateness, feasibility, fidelity, adoption, sustainability, satisfaction, and usage.MethodsA hybrid type I effectiveness-implementation trial will be conducted. A cluster randomized controlled trial will be used to assess the effectiveness of `Saga Stories in health talks´ in 42 CHC centers across six regions in Sweden. `Saga Stories in health talks´ consists of material for CHC nurses to use to facilitate the health talk with both the child and parent(s) and is complemented with take-home material. Parent and child dyads are recruited (n = 450) from participating CHC centers when they attend their 5-year routine visit. The intervention group receives the health talk using Saga Stories and take-home material, whereas the control group receives the standard health talk. The primary outcome is parental self-efficacy to promote healthy diet, physical activity, and screen time behaviours in their child and secondary outcomes include children’s intake of key dietary indicators and screen time. All outcomes are assessed at baseline and 2-months post-intervention. The implementation outcomes that will be assessed are: acceptability, appropriateness, feasibility, satisfaction, usage, fidelity, adoption, and sustainability (assessed quantitatively and qualitatively).DiscussionThe Swedish National Board of Health and Welfare have identified the need of more material, education, and working methods for promoting healthy lifestyle behaviours in CHC. Following this trial `Saga Stories in health talks´ has great potential to be implemented in CHC across Sweden to aid nurses to promote and support healthy lifestyle behaviours in pre-school children and their families.Trial registrationClinicalTrials.gov,NCT05237362. Registered 2 February 2022.