Privately insured US children account for 40% of non-birth-related pediatric hospitalizations. However, there are no national data on the magnitude or correlates of out-of-pocket spending for these hospitalizations. To estimate out-of-pocket spending for non-birth-related hospitalizations among privately insured children and identify factors associated with this spending. This study is a cross-sectional analysis of the IBM MarketScan Commercial Database, which reports claims from 25 to 27 million privately insured enrollees annually. In the primary analysis, all non-birth-related hospitalizations of children 18 years and younger from 2017 through 2019 were included. In a secondary analysis focused on insurance benefit design, hospitalizations that could be linked to the IBM MarketScan Benefit Plan Design Database and were covered by plans with a family deductible and inpatient coinsurance requirements were analyzed. In the primary analysis, factors associated with out-of-pocket spending per hospitalization (sum of deductibles, coinsurance, and copayments) were identified using a generalized linear model. In the secondary analysis, variation in out-of-pocket spending was assessed by level of deductible and inpatient coinsurance requirements. Among 183 780 hospitalizations in the primary analysis, 93 186 (50.7%) were for female children, and the median (IQR) age of hospitalized children was 12 (4-16) years. A total of 145 108 hospitalizations (79.0%) were for children with a chronic condition and 44 282 (24.1%) were covered by a high-deductible health plan. Mean (SD) total spending per hospitalization was $28 425 ($74 715). Mean (SD) and median (IQR) out-of-pocket spending per hospitalization were $1313 ($1734) and $656 ($0-$2011), respectively. Out-of-pocket spending exceeded $3000 for 25 700 hospitalizations (14.0%). Factors associated with higher out-of-pocket spending included hospitalization in quarter 1 compared with quarter 4 (average marginal effect [AME], $637; 99% CI, $609-$665) and lack of chronic conditions compared with having a complex chronic condition (AME, $732; 99% CI, $696-$767). The secondary analysis included 72 165 hospitalizations. Among hospitalizations covered by the least generous plans (deductible of $3000 or more and coinsurance of 20% or more) and most generous plans (deductible less than $1000 and coinsurance of 1% to 19%), mean (SD) out-of-pocket spending was $1974 ($1999) and $826 ($798), respectively (AME, $1123; 99% CI, $1069-$1179). In this cross-sectional study, out-of-pocket spending for non-birth-related pediatric hospitalizations were substantial, especially when they occurred early in the year, involved children without chronic conditions, or were covered by plans with high cost-sharing requirements.