BackgroundWhilst the global burden of caries is increasing, the trajectory of decay in young children and the point at which prevention should occur has not been well established.AimTo identify the ‘natural history’ of dental caries in early childhood.DesignA birth cohort study was established with 467 mother/child dyads followed at 1, 6, 12, 18, and 36 months of age. Parent‐completed surveys captured demographic, social, and behavioural data, and oral examinations provided clinical and data.ResultsEight per cent of children (95% confidence interval (CI): 5–12%) at 18 months and 23% (95% CI: 18–28%) at 36 months experienced decay. Interesting lesion behaviour was found between 18 and 36 months, with rapid development of new lesions on sound teeth (70% of teeth, 95% CI: 63–76%) and regression of many lesions from non‐cavitated lesions to sound (23% of teeth, 95% CI: 17–30%). Significant associations were found between soft drink consumption and lesion progression.ConclusionsFindings suggest optimal time periods for screening and prevention of a disease which significantly impacts multiple health and well‐being outcomes across the life course.