The aim of the study was to identify dietary patterns (DP) and examine differences in anthropometric measures, blood pressure (BP), cardiorespiratory fitness and nutritional knowledge of 6- and 10-year-old children at baseline and following a nutrition and physical activity intervention, with respect to DP and treatment group. This is a longitudinal study. Food diary, nutritional knowledge questionnaire and 550-m walk/run test measured dietary intake, nutritional knowledge and cardiorespiratory fitness, respectively. BP, weight, height and waist circumference were also measured and BMI and waist-to-height ratio (WHtR) were derived. All measurements were performed at baseline and following intervention. Two primary schools (one intervention, one control) in Cork, Ireland, were selected. Participants were 6- (n 39, age 5·9 (sd 0·6) years) and 10- (n 49, age 9·8 (sd 0·5) years)-year-olds. Two DP were identified, using k-means cluster analysis, for both 6- (unhealthy and nutrient-dense) and 10-year-olds (processed and Western diet) at baseline. DP derived post-intervention were (1) plant-based and (2) processed foods for 6-year-olds and (1) nutrient-dense and (2) unhealthy for 10-year-olds. There was no statistically significant difference in DP for 6- and 10-year-olds at baseline and post-intervention (P > 0·05). Following the intervention, a multivariate ANOVA showed there were no statistically significant differences in nutritional knowledge, BMI, WHtR, cardiorespiratory fitness and BP based on DP and intervention/control group for both age groups (P > 0·05). Three out of four dietary patterns identified for 6- and 10-year-olds were unfavourable. While no statistically significant evidence of intervention impact was found on DP, a positive trend was emerging among 10-year-olds.