Tooth decay which is the most common nutrition-related disease, was the focus of this study. Here, we investigated the association between diet, obesity, and dental caries in young children. This descriptive-analytical study included the assessment of children’s oral health through the DMFT index to determine tooth decay. Body mass index was used to calculate the level of obesity, and a semi-quantitative food frequency questionnaire (FFQ) assessed food consumption patterns. The findings showed that overweight and obese young children had a significantly higher caries index compared to their peers (P < 0.05). Analysis of food consumption frequency showed that, except for dairy products, most children included fruits and vegetables in their diets. An inverse relationship was found between tooth decay and the consumption of milk, dairy, fruits, and vegetables, while a strong positive correlation was observed between BMI and the frequency of sweets consumption. This study identifies obesity, high intake of cariogenic snacks, and low consumption of fruits, vegetables, and dairy products as important risk factors for dental caries in children. Given the vital role of dental health in overall well-being, it is essential to educate parents and children about the importance of maintaining a balanced diet.