Background <p>Legumes can substitute for meat and are thus a particularly important food group for environmental sustainability. As the use of legumes among Finnish children is marginal, there is potential for a substantial increase in their consumption. However, food education delivered through early childhood education and care (ECEC) settings has rarely focused specifically on environmentally sustainable foods, such as legumes. This study describes the implementation and effectiveness of an ECEC-delivered food education intervention within the FoodStep study.</p> Methods <p>The partially cluster-randomized FoodStep intervention aimed to increase the supply of vegetables, legumes, fruits, berries, and sustainable fish while reducing the provision of other animal-based foods in the intervention ECEC centres. The control centres maintained their regular menus. Food education materials and training were included to support the acceptability of the menu changes. Based on implemented food education activities reported by the ECEC professionals during the 10-month intervention, the ECEC centres were classified into high-intensity intervention (<i>n</i> = 5), low-intensity intervention (<i>n</i> = 6), and control group (<i>n</i> = 12). Parents of the participating 3- to 5-year-old children (<i>n</i> = 86) reported their child’s willingness to taste foods using a five-point scale. Food consumption was assessed using two separate food frequency questionnaires: (1) foods consumed outside ECEC and (2) foods consumed in ECEC. We used linear mixed models to examine the effectiveness of the food education intervention in increasing food acceptance and consumption.</p> Results <p>Commonly implemented food education activities were sensory food education, books and drama, gardening, and crafting. Compared with the control group, the children in the high-intensity intervention group showed higher acceptance of (β = 4.27, 95% CI − 0.03 to 8.57, <i>p</i> = 0.06), and consumed more, legumes at the follow-up (β = 1.18, 95% CI 0.31 to 2.06, <i>p</i> = 0.01). No statistically significant associations were observed for the other food groups.</p> Conclusions <p>ECEC-delivered food education interventions accompanied by accessible materials and activities can help to promote sustainable diets in children by increasing the acceptability and consumption of environmentally sustainable foods, such as legumes. To encourage sustainable diets, menu modifications should be supplemented with pedagogic food education activities in ECEC centres.</p> Trial registration <p>ClinicalTrials.gov (NCT05249946) November 29, 2021.</p>