Objectives: With 60–90% of children worldwide reportedly experiencing dental caries, poor oral health in the younger years is a major public health issue. As parents are important to children's oral hygiene practices, we examined the key self‐regulatory behaviours of parents for supervising their children's toothbrushing using the health action process approach. Design and method: Participants (N = 281, 197 mothers) comprised Australian parents of 2‐ to 5‐year‐olds. A longitudinal design was used to investigate the sequential mediation chain for the effect of intention (Time 1) on parental supervision for their youngest child's toothbrushing (Time 3), via self‐efficacy and planning (Time 2), and action control (Time 3). Results: A latent‐variable structural equation model, controlling for baseline behaviour and habit, revealed significant indirect effects from intention via self‐efficacy and action control and intention via planning and action control, on parental supervision behaviour. The model was a good fit to the data, explaining 74% of the variance in parents’ supervising behaviour for their children's toothbrushing. Conclusion: While national recommendations are provided to guide parents in promoting good oral hygiene practices with their children, current results show the importance of going beyond simple knowledge transmission to support parents’ intentions to supervise their children's toothbrushing actually materialize. Current findings make a significant contribution to the cumulative empirical evidence regarding self‐regulatory components in health behaviour change and can inform intervention development to increase parents’ participation in childhood oral hygiene practices, thus helping to curb rising oral health conditions and diseases.