Purpose: In light of the latest epidemiological and nutritional knowledge and scientific evidence supporting responsive feeding, the French feeding guidelines for 0-3 years were recently updated and nationally disseminated through a brochure and media campaign by Santé publique France. Moreover, smartphone apps become increasingly popular and is likely relevant to provide timely information across development to inform parents about child feeding practices but their effect is seldom evaluated. This randomized controlled trial (RCT) aims to investigate whether the provision of guidelines through an app and a brochure (vs. brochure alone, usual service) results in healthier parental feeding practices, infant's eating behaviours and body mass index (BMI). Methods: This double-blinded monocentric 2-arm trial is conducted among first-time parents living in the area of Dijon (France) and recruited in a maternity ward. A smartphone app was developed by INRAE for the outcome evaluation and for the timely distribution of the new guidelines content: from child age 3 to 36 months, 106 age-adapted messages with dietary recommendations, educational advice, recipes and tips provided in the form of short texts and videos (intervention group only), and 36 generic messages (both groups). The primary outcome is the BMI z-score at 36 months of age. Secondary outcome measures include online parents' reports and behavioural assessments (experimental meals) of parental feeding practices and infant eating behaviours from inclusion to 36 months of age. Analyses of covariance on these outcomes will assess the effect of the intervention. Mediation and moderation analyses will explore, respectively, the mechanisms of action of the intervention and the potential moderating effect of socioeconomic, parental (attitudes and beliefs about child feeding) and infants' (general temperament) factors. Sample size was determined to be n=118 in each arm, plus 20% to compensate for potential attrition.Results/findings: The first participants were enrolled in March 2022 and the recruitment is ongoing (n=110 were included on February 2023). Conclusions: This is the first French RCT to assess a digital intervention targeted to first-time parents to improve feeding practices and child growth. The app may represent a potential stand-alone communication tool to complement those already disseminated to the general population.