Elevated serum uric acid levels are the essential pathophysiology of gout. Although gout rarely develops in childhood, chronic persistent hyperuricemia can induce precipitation and deposition of sodium urate crystals, leading to the development of gout. Hyperuricemia is caused by increased uric acid production and/or decreased uric acid excretion capacity of the kidneys and/or intestinal tract. Increased production of uric acid, the final metabolite of purine, is associated with an increase of phosphoribosyl pyrophosphate, the key compound in the purine synthesis pathways, as observed in hypoxanthine-guanine phosphoribosyltransferase deficiency. Another mechanism for increased uric acid production is increased adenosine triphosphate consumption that is found in glycogen storage disease type I. On the other hand, in uromodulin-associated kidney disease, the accumulation of abnormal uromodulin in the kidneys leads to tubulointerstitial damage and fibrosis, and the ability to excrete uric acid is compromised, with reduced secretion and increased reabsorption in the proximal tubules. Decreased uric acid excretion from the kidneys or intestinal tract is also mediated by decreased function of the ATP-binding cassette subfamily G member 2, a urate transporter that acts in the urate secretion. This review summarizes the selected pathophysiological mechanisms underlying the genetic basis of hyperuricemia and gout in children, both in terms of purine metabolism and uric acid excretion.