Abstract Background Most children fail to meet recommended guidelines for a healthy diet. Children living in low socioeconomic areas are less likely to have healthy eating behaviours. In this study we investigated the food Dutch primary school children bring from home, and their dietary, health and school related outcomes explored by sociodemographics. Methods 5 primary schools, with high deprivation scores and a high percentage of overweight, have been included in this study (ClinicalTrials.gov NCT06058325). With observations in September 2023 we mapped the content of lunchboxes, including snacks, of children. Questionnaires for all parents and children in grade 5-8 focused on dietary and health outcomes of children and perceived class factors. Preliminary baseline data were analysed using descriptive statistics. Exploratory analyses will be conducted to show differences by sociodemographics (e.g. age, sex, parental financial stress). Results 297 lunchboxes were observed, 98.7% contained sandwiches, half being brown bread. Most children brought fruit from home for either lunch or morning snack, 13.8% not at all. 21.9% brought vegetables. 135 children completed the questionnaire: 43.0% boys, mean age 9.3 years old (SD 1.12). Children ate fruit and vegetables on an average of 5.9 (SD 1.69) and 4.9 (SD 2.23) days a week. Whereas 80% of children eats fruit every day at school, only 20% of children eats vegetables every day at school. Most children perceived their health as good (89.3%) and felt happy (89.6%). On a scale of 1 (low) to 5 (high), they rated concentration, social climate and comfort in class an average of 3.8 (SD 1.05), 4.3 (SD 1.07) and 4.3 (SD 0.92) respectively. Conclusions Lunchboxes of Dutch primary school children mainly contain sandwiches. Whereas most children eat fruit at school, the majority of children do not eat vegetables at school. A healthy school lunch might increase vegetable consumption of children and could affect health and school related outcomes. Key messages • Most Dutch primary school children eat sandwiches during lunch at school, but in half of the cases this is not brown bread as recommended by nutritional guidelines. • Most Dutch primary school children bring fruit to eat as snack or lunch, but no vegetables to eat at school. The majority also self-reported the lack of eating vegetables at school on a daily basis.