Background: Same-day surgery implies patient discharge on the same day after the surgery. The main aim of the research was to determine which predisposing factors lead to children treated with same-day surgery not being able to be discharged on the same day. Methods: For the purposes of this research, the electronic records of patients in the hospital information system were reviewed retrospectively. The search included patients who were surgically treated through the Day Surgery Unit at the Children’s Hospital Zagreb with various diagnoses from 1 January 2021 to 31 December 2023. The target group consisted of patients who could not be discharged on the same day (n = 68), while for the purposes of the control group (n = 68), patients were randomly selected, comparable by age and gender, who were discharged from the hospital on the same day in accordance with the principles of same-day surgery. Results: In relation to the parameters of interest between the groups, statistically significant differences were observed in the type of general anesthesia (p = 0.027), the use of analgesics (p = 0.016), the time of entering the operating room (p = 0.000), the time of leaving the operating room (p < 0.0001) and the duration of surgery (76.81 ± 37.21 min vs. 46.51 ± 22.46 min., p < 0.0001). When explanatory variables were included in the regression model, they explained 38% of the variability in the dependent variable. Only the variable “duration of surgery” provided significant information to explain the variability in the dependent variable (p = 0.004). Conclusions: Although the duration of surgery was imposed as the main predictor of hospitalization after same-day surgery, and considering the extremely small number of studies on the mentioned topic, especially in the pediatric population, further, preferably multicenter research on the mentioned topic is needed.