Validation of KIDMED 2.0 PL—Mediterranean Diet Quality Index for Polish Children and Adolescents

Background: The Mediterranean diet is widely recognised for its health benefits and remains a key reference point in shaping dietary guidelines across populations. Despite its growing international relevance, there is a lack of validated tools assessing Mediterranean diet adherence among children and adolescents in Central and Eastern Europe. Methods: The present study aimed to adapt and validate the KIDMED 2.0 questionnaire for use in Polish children and adolescents aged 10 to 18 years (KIDMED 2.0 PL). The adaptation process involved forward–backward translation, expert consultations, and pilot testing to ensure linguistic and cultural relevance. A total of 102 participants completed the questionnaire twice over a two-week interval, and anthropometric data were collected. Results: The KIDMED 2.0 PL demonstrated high test–retest reliability (Spearman’s ρ = 0.876; p < 0.001) and strong criterion validity, with a significant negative correlation between KIDMED scores and BMI centile (ρ = −0.854; p < 0.001). Children with normal weight showed the highest adherence to the Mediterranean diet, while scores were significantly lower in overweight and obese participants. Item-level analysis indicated that fruit and vegetable consumption was relatively frequent, whereas intake of legumes, whole grains, and extra virgin olive oil remained low. Conclusion: The KIDMED 2.0 PL is a valid and reliable tool for evaluating diet quality and Mediterranean dietary adherence in the Polish pediatric population.