IntroductionParents shape child emotional competence and mental health via their beliefs about children’s emotions, emotion-related parenting, the emotional climate of the family and by modelling emotion regulation skills. However, much of the research evidence to date has been based on small samples with mothers of primary school-aged children. Further research is needed to elucidate the direction and timing of associations for mothers and fathers/partners across different stages of child development. The Child and Parent Emotion Study (CAPES) aims to examine longitudinal associations between parent emotion socialisation, child emotion regulation and socioemotional adjustment at four time points from pregnancy to age 12 years. CAPES will investigate the moderating role of parent gender, child temperament and gender, and family background.Methods and analysisCAPES recruited 2063 current parents from six English-speaking countries of a child 0–9 years and 273 prospective parents (ie, women/their partners pregnant with their first child) in 2018–2019. Participants will complete a 20–30 min online survey at four time points 12 months apart, to be completed in December 2022. Measures include validated parent-report tools assessing parent emotion socialisation (ie, parent beliefs, the family emotional climate, supportive parenting and parent emotion regulation) and age-sensitive measures of child outcomes (ie, emotion regulation and socioemotional adjustment). Analyses will use mixed-effects regression to simultaneously assess associations over three time-point transitions (ie, T1 to T2; T2 to T3; T3 to T4), with exposure variables lagged to estimate how past factors predict outcomes 12 months later.Ethics and disseminationEthics approval was granted by the Deakin University Human Research Ethics Committee and the Deakin University Faculty of Health Human Research Ethics Committee. We will disseminate results through conferences and open access publications. We will invite parent end users to co-develop our dissemination strategy, and discuss the interpretation of key findings prior to publication.Trial registerationProtocol pre-registration: DOI 10.17605/OSF.IO/NGWUY.