Background There are limited studies on the necessity of preoperative antibiotics in surgeries for undescended testis (UDT), inguinal hernia (IH), and umbilical hernia (UH) in children. Here, we investigated the relationship between preoperative antibiotic use and surgical site infection (SSI) incidence in surgeries for UDT, IH, and UH in children. Methods Patients who underwent surgery for IH were subdivided based on the surgical form into those who underwent (i) open IH (OIH) repair and (ii) laparoscopic percutaneous extraperitoneal closure (LPEC). Medical records of patients who underwent surgeries for UDT and IH or UH were retrospectively examined. The SSI incidence was compared between patients receiving and not receiving preoperative antibiotics. In patients who underwent surgery for UH or LPEC, the relative risk of SSI postoperatively in the inguinal region (including surgery for UDT and OIH repair) was examined. Results In total, 926 patients with 1389 wounds were included in this study. SSI rates in patients who underwent surgeries for UDT and UH, OIH repair, and LPEC were 0.2% and 2.7%, 0.3%, and 0.4%, respectively. These rates were not significantly different between patients receiving and not receiving preoperative antibiotics. In patients who underwent surgery for UH, the relative risk of SSI was statistically significant at 9.8 compared with that in patients who underwent surgeries in the inguinal region (95% CI = 1.3-74; p = 0.013). Conclusions Preoperative antibiotics are unnecessary in surgeries for UDT and OIH repair. Patients undergoing surgery for UH should be given extensive care as they are at a high risk of SSI.