Introduction and objective: Tuberous sclerosis complex is a rare genetic disorder characterized by benign tumours in multiple organs (e.g., brain, kidneys). The affected patients present with kidney tumours, including angiomyolipomas and cysts, rarely other lesions, including renal cell carcinoma. This study aimed to evaluate renal lesions, renal function, and blood pressure in children managed in our Centre between 2018 and 2023. Materials and methods: We looked at the presence and size of kidney lesions (ultrasonography, magnetic resonance), genetic findings, blood pressure, and biochemical parameters, including kidney function (GFR calculated from the Schwartz formula) in 55 pediatric patients (28 boys, 27 girls, 8.1 ± 4.6 years). Results: Angiomyolipomas were found in 40/55 (72.7%) patients, including fat-poor (atypical) angiomyolipomas in 9 (16.4%) children. The mean angiomyolipoma size was 13.1 ± 15.1 mm; large angiomyolipomas ≥30 mm were present in 5 (9.1%) children. Cysts were found in 46 (83.6%) children; the mean cyst size was 10.3 ± 12.3 mm. The largest cysts (up to 75 mm) were found in 4 children with contiguous gene syndrome (deletion involving two genes: TSC2 and PKD1). Seven (12.7%) children had arterial hypertension, including 3 out of 4 children with contiguous gene syndrome. Mean GFR was 111.2 ± 17.1 mL/min/1,73 m², and GFR <90 mL/min/1,73 m² was found in 3 (5.5%) children (2 with contiguous gene syndrome). Patients with hypertension had higher triglyceride concentrations, larger kidney longitudinal dimensions, and larger cysts (22.6 ± 27.1 vs. 8.0 ± 5.3 mm). The size of angiomyolipoma correlated with age (r = 0.470, p <0.001) and urinary albumin-creatinine ratio (r = 0.444, p = 0.001). Conclusions: 1. Large renal lesions are common already in children with tuberous sclerosis complex, with the most severe renal manifestations found in patients with contiguous gene syndrome. 2. The size of angiomyolipoma increases with age in children with tuberous sclerosis complex. 3. Large angiomyolipomas are risk factors for elevated urinary albumin excretion. 4. In paediatric patients with tuberous sclerosis complex, large cysts are risk factors for arterial hypertension. 5. Paediatric nephrologists should follow up all pediatric patients with tuberous sclerosis complex.