Introduction and objective: Crohn’s disease (CD) and ulcerative colitis (UC), which often impact individuals in their youth, significantly affect quality of life. This study analyses anthropometric data and clinical presentations of CD and UC over a 13-year period in newly diagnosed patients at the Department of Paediatric Gastroenterology and Hepatology in Zabrze, Poland. Materials and methods: Seventy-four CD patients and 90 UC patients were analysed, and categorised into four groups based on disease type and diagnosis period: Group A (CD, 2008–2011), Group B (CD, 2018–2021), Group C (UC, 2008–2011), and Group D (UC, 2018– 2021). Collected data encompassed gender, age, weight, height, body mass index (BMI), duration of symptoms before diagnosis, disease location, and activity. Results: Among patients diagnosed between 2018 and 2021 (Groups B and D), CD exhibited a higher prevalence in boys (67.57% vs. 32.43%), while UC was more prevalent in girls (61.40% vs. 38.60%). Groups A and B demonstrated lower mean weight standard deviation scores (SDS) and BMI-SDS compared to Groups C and D. Symptom duration before diagnosis was shorter in Group C than in Group A (5 vs. 10 months) and in Group D compared to Group B (6 vs. 11 months). Severe CD activity at diagnosis was higher in Group A than in Group B (35.14% vs. 5.41%). The results were statistically significant – p < 0.05. Conclusions: UC diagnoses remain faster than CD, possibly due to more alarming symptoms. Patients diagnosed with CD demonstrate lower body weight and BMI compared to UC patients. The incidence of severe CD activity has significantly decreased over 13 years, potentially due to enhanced paediatric care and expedited diagnosis.