Objectives: To estimate the proportion of infants introduced to peanut and other common food allergens by 12 months of age; to collect information about parent-reported reactions to food. Design, setting: Observational cohort study, applying the SmartStartAllergy SMS protocol and online questionnaire to parents of 12-month-old infants attending 69 Australian general practices between 21 September 2018 and 3 May 2019. Participants: 3374 parents recruited via the 69 participating general practices. Main outcome measures: Proportions of infants who had eaten peanut and other common food allergens; proportions with parent-reported reactions to food. Results: 1940 of 3374 invited parents participated in the study (response rate, 57%), of whom 836 (46%) completed the online questionnaire. At 12 months of age, 1673 of 1940 infants had eaten peanut-including foods (86.2%; 95% confidence interval [CI], 84.6–87.7%); 235 of 1831 parents (12.8%; 95% CI, 11.3–14.5%) reported food-related reactions. Questionnaire responses indicated that dairy was the food type most frequently reported to cause a food-related reaction (72 of 835 exposed infants, 8.6%; 95% CI, 6.8–11%); peanut-related reactions were reported for 20 of 764 exposed children (2.6%; 95% CI, 1.6–4.0%). 97 of 250 parent-reported reactions to food (39%) did not include symptoms that suggested an IgE-mediated allergic reaction. Conclusion: Infant feeding practices in Australia have changed over the past decade; a large majority of infants are now fed peanut before 12 months of age. The SmartStartAllergy program allows monitoring of infant feeding practices in primary care, as well as of parent-reported reactions to food in infants.