Background The purpose of this study was to compare the clinical symptoms and pathological consequences of Helicobacter pylori (H. pylori) infection between children and adults and determine the levels of expression of FOX3P and IL‐17A to examine the Th17/Treg balance. Methods Forty pediatric and 40 adult patients who were followed up at the Pediatric Gastroenterology and Internal Medicine Gastroenterology Departments were enrolled in the study. In our case‐control study, gastric tissue specimens were evaluated using the updated Sydney system, and the number of cells expressing FOXP3/IL‐17A (Treg and Th17 cell markers) was analyzed immunohistochemically. In addition, each case was evaluated using a clinical follow‐up questionnaire. Results Clinical signs and symptoms of children and adults were similar. IL‐17A and FOXP3 levels were significantly higher in children and adults with H. pylori (+) than in those without H. pylori (−) (p < .001). In patients with H. pylori (+), the mean FOXP3 level was significantly higher, whereas the mean IL‐17A level was significantly lower in children than in adults (p < 0001 for both groups). In children with H. pylori (+), bacterial density was negatively correlated with IL‐17A level and positively correlated with FOXP3 level. In adults with H. pylori (+), there was a statistically significant, highly positive correlation between bacterial density and levels of IL‐17A and FOXP3. Conclusions Treg cells are suggested to more predominant in children than in adults, IL‐17A levels decrease as H. pylori bacterial density increases. In conclusion, immune responses incline toward Treg, which increases the susceptibility to persistent infections.