Background Surgical care is an important, yet often neglected component of child health in low- and middle-income countries (LMICs). This study examines the potential impact of scaling up surgical care at first-level hospitals in LMICs within the first 20 years of life. Methods Epidemiological data from the global burden of disease 2019 Study and a counterfactual method developed for the disease control priorities; 3rd Edition were used to estimate the number of treatable deaths in the under 20 year age group if surgical care could be scaled up at first-level hospitals. Our model included three digestive diseases, four maternal and neonatal conditions, and seven common traumatic injuries. Results An estimated 314,609 (95% UI, 239,619–402,005) deaths per year in the under 20 year age group could be averted if surgical care were scaled up at first-level hospitals in LMICs. Most of the treatable deaths are in the under-5 year age group (80.9%) and relates to improved obstetrical care and its effect on reducing neonatal encephalopathy due to birth asphyxia and trauma. Injuries are the leading cause of treatable deaths after age 5 years. Sixty-one percent of the treatable deaths occur in lower middle-income countries. Overall, scaling up surgical care at first-level hospitals could avert 5·1% of the total deaths in children and adolescents under 20 years of age in LMICs per year. Conclusions Improving the capacity of surgical services at first-level hospitals in LMICs has the potential to avert many deaths within the first 20 years of life.