Background: Familial hypercholesterolemia (FH) is a genetic autosomal co-dominant metabolic disorder leading to elevated circulating concentrations of low-density lipoprotein cholesterol (LDL-C). Early development of atherosclerotic cardiovascular disease (ASCVD) is common in affected patients. We aimed to evaluate the characteristics and differences in the diagnosis and therapy of FH children and adults. Methods: All consecutive patients who were diagnosed with FH, both phenotypically and with genetic tests, were included in this analysis. All patients are a part of the European Atherosclerosis Society FH-Study Collaboration (FHSC) regional center for rare diseases at the Polish Mother’s Memorial Hospital Research Institute (PMMHRI) in Lodz, Poland. Results: Of 103 patients with FH, there were 16 children (15.5%) at mean age of 9 ± 3 years and 87 adults aged 41 ± 16; 59% were female. Children presented higher mean levels of total cholesterol, LDL-C, and high-density lipoprotein cholesterol (HDL-C) measured at the baseline visit (TC 313 vs. 259 mg/dL (8.0 vs. 6.6 mmol/L), p = 0.04; LDL 247 vs. 192 mg/dL (6.3 vs. 4.9 mmol/L), p = 0.02, HDL 53 vs. 48 mg/dL (1.3 vs. 1.2 mmol/L), p = 0.009). Overall, 70% of adult patients and 56% of children were prescribed statins (rosuvastatin or atorvastatin) on admission. Combination therapy (dual or triple) was administered for 24% of adult patients. Furthermore, 13.6% of adult patients and 19% of children reported side effects of statin therapy; most of them complained of muscle pain. Only 50% of adult patients on combination therapy achieved their treatment goals. None of children achieved the treatment goal. Conclusions: Despite a younger age of FH diagnosis, children presented with higher mean levels of LDL-C than adults. There are still urgent unmet needs concerning effective lipid-lowering therapy in FH patients, especially the need for greater use of combination therapy, which may allow LDL-C targets to be met in most of the patients.