Family screen use rules (FSRs) could plausibly protect against the development of childhood obesity, although the mechanisms underlying these protective effects remain largely unexplored. This research aimed to investigate prospectively the associations between exposure to FSRs at age 24 months, obesogenic behaviours (excessive screen time and short sleep duration) at age 45 months, and obesity at age 54 months. Additionally, a model proposing the mediating role of obesogenic behaviours in the association between FSRs and childhood obesity was tested. Data were obtained from 5733 children and their mothers participating in the 'Growing Up in New Zealand' study. Logistic regressions examined the association between three FSRs (rules on quality, quantity and timing of screen time, and different numbers of FSRs), obesogenic behaviours, and childhood obesity. Structural equation modelling (SEM) was applied to assess the potential mediating roles of obesogenic behaviours in the association between FSRs and zBMI. Neither exposure to individual nor all three FSRs was significantly associated with lower odds of obesity. However, protective effects of FSRs were observed concerning obesogenic behaviours. Exposure to individual or all three FSRs correlated with reduced odds of not meeting screen time and sleep duration recommendations. SEM analysis indicated no direct association between FSRs and zBMI
nevertheless, a significant indirect association was identified through the mediation of obesogenic behaviours. These findings suggest the potential benefits of promoting the adoption of FSRs as a promising population-based strategy to enhance child health behaviours and mitigate the risk of childhood obesity.