Purpose: Base deficit (BD) is superior to vital signs in predicting trauma outcomes in adults. The authors aimed to compare BD and vital signs as criteria for the four-tiered hemorrhagic shock classification in children with trauma. Materials and Methods: We retrospectively reviewed the data of 1046 injured children who visited a Korean academic hospital from 2010 through 2018. These children were classified separately based on BD (class I, BD ≤2.0 mmol/L; II, 2.1–6.0 mmol/L; III, 6.1–10 mmol/L; and IV, ≥10.1 mmol/L) and vital signs (<13 years: age-adjusted hypotension and tachycardia, and Glasgow Coma Scale; 13–17 years: the 2012 Advanced Trauma Life Support classification). The two methods were compared on a class-by-class basis regarding the outcomes: mortality, early transfusion (overall and massive), and early surgical interventions for the torso or major vessels. Results: In total, 603 children were enrolled, of whom 6.6% died. With the worsening of BD and vital signs, the outcome rates increased stepwise (most p<0.001; only between surgical interventions and vital signs, p=0.035). Mortality more commonly occurred in BD-based class IV than in vital signs-based class IV (58.8% vs. 32.7%, p=0.008). Early transfusion was more commonly performed in BD-based class III than in vital signs-based class III (overall, 73.8% vs. 53.7%, p=0.007; massive, 37.5% vs. 15.8%, p=0.001). No significant differences were found in the rates of early surgical interventions between the two methods. Conclusion: BD can be a better predictor of outcomes than vital signs in children with severe hemorrhagic shock.