This study aimed to evaluate the effectiveness of combining initial hemoglobin levels with the shock index for predicting the need for life-saving interventions (LSI) in pediatric patients with blunt liver and spleen injuries (BLSI), specifically tailored to different age groups. This was a multicenter retrospective cohort study of pediatric patients with BLSI in Japan. The area under the receiver operating characteristic curve (AUROC) were used to assess predictive accuracy. The study included 1,370 patients. LSI was required in 59 of 247 (23.9%) aged 1 to 6 years, 100 of 402 (24.9%) aged 7 to 12 years, and 125 of 297 (42.1%) patients aged 13 to 16 years. Within each specific age group, the predictability was categorized as fair and appeared higher than that of the entire cohort or when using either parameter alone. Notably, in the 1 to 6-year age group, the combined values showed the highest predictability, which was statistically superior to the shock index alone (AUROC of 0.770 vs. 0.671, P = 0.025). Tailoring initial hemoglobin levels and shock index to specific age groups enhances predictability of LSI in pediatric BLSI, showing a fair level of predictive accuracy.