ObjectiveThe aim of this study is to identify risk factors associated with acute complicated appendicitis (CA) in children aged three years or younger, providing a theoretical foundation for the management and treatment of acute appendicitis (AA).MethodsA retrospective analysis was conducted on 135 pediatric patients with AA, admitted to the Department of General Surgery at Anhui Children’s Hospital between December 2020 and December 2023, who underwent successful surgical treatment. Based on the intraoperative and postoperative pathological findings, patients were categorized into two groups: complicated appendicitis (CA) (n = 97 cases) and uncomplicated appendicitis (UA) (n = 38 cases). Clinical data including gender, age, weight, disease duration, preoperative white blood cell count (WCC), neutrophil granulocyte (NEUT) count, C-reactive protein (CRP) levels, total bilirubin (TBil) levels, procalcitonin (PCT) levels, calprotectin (Cal) levels, preoperative ultrasound results indicating the presence or absence of fecaliths, maximum appendix diameter, and pediatric appendicitis sore (PAS) were collected and analyzed. Comparative analysis was performed to investigate the differences between the groups and identify risk factors of CA.ResultsThe CA group exhibited significantly higher values in disease duration, CRP levels, PCT, Cal, presence of appendiceal fecaliths, maximum appendix diameter, and PAS compared to the UA group (P < 0.05). Multivariate analysis identified CRP levels, maximum appendix diameter, and PAS as independent risk factors for CA. Specifically, differences in CRP level (OR = 1.045, 95% CI:1.024 ~ 1.067, P < 0.001), PAS (OR = 1.768, 95% CI:1.086 ~ 2.879, P = 0.022), and maximum appendix diameter (OR = 1.860, 95% CI:1.085 ~ 3.191, P = 0.024) were significant. The area under the receiver operating characteristic curve values were 0.6776 for the PAS, 0.7663 for CRP, and 0.5604 for the maximum appendix diameter.ConclusionCRP levels, PAS, and maximum appendix diameter are independent risk factors for CA in children under three years of age. These parameters are valuable for the early diagnosis of CA.