Introduction – The Court of Auditors recently highlighted a lack of information regarding health inequalities among children. This cross-sectional observational study, based on the National Health Data System (SNDS), compares the prevalence of long-term conditions (ALD) and hospital diagnoses—including preventable ones—according to the level of social disadvantage. Methods – All children in mainland France under the age of 18 at the end of 2018 who had received at least one reimbursement were included based on their birth month and then followed for 1 year. The prevalence of ALDs and hospital diagnoses was reported according to whether or not households with incomes below the poverty line were assigned supplementary universal health coverage (CMUc). Geographical social disadvantage was estimated using an index (FDep) divided into 5 quintiles: from the most advantaged municipalities (Q1) to the most disadvantaged (Q5). Adjusted ratios between CMUc/non-CMUc and Q5/Q1 allowed for a comparison of disease levels according to social disadvantage. Results – The distribution of the 13.211 million children included was homogeneous across the quintiles, and 17.5% had CMUc. At least one ALD was present in 4% of children (ratios CMUc/non-CMUc = 1.6 and Q5/Q1 = 1.44). Among the 10 most common ALDs, 6 corresponded to a mental disorder, with higher ratios for CMUc. Certain hospital diagnoses were more frequent among disadvantaged children, such as mental disorders, blood diseases, and dental caries. The proportion of avoidable hospitalizations among children aged 0 to 10 was 26% (Q5/Q1 = 1.15). Conclusion – Many conditions are more common in the presence of social disadvantage (especially financial), particularly mental disorders. However, identifying them remains difficult due to a lack of data collection or comprehensiveness at specialized pediatric centers within the SNDS.