Importance Assessment of the quality of initial care is necessary to target priority actions that can reduce the still high morbidity and mortality due to community-onset severe bacterial infections (COSBIs) among children. Objective To study the prevalence, characteristics, and determinants of suboptimal care in the initial management of COSBIs. Design, Setting, and Participants This prospective, population-based, cohort study and confidential enquiry was conducted between August 2009 and January 2014 in western France, a region accounting for 15% of the French pediatric population (1 968 474 children aged 1 month to 16 years) and including 6 pediatric intensive care units (PICUs) and 35 emergency departments. Participants included all children aged 1 month to 16 years who died before PICU admission or were admitted to a PICU with a COSBI (ie, bacterial sepsis, including meningitis, purpura fulminans, and pulmonary, osteoarticular, intra-abdominal, cardiac, and soft-tissue severe infections). Data were analyzed from March to June 2020. Exposures Suboptimal care determined according to evaluation of 8 types of care: (1) the delay in seeking care by family, (2) the physician’s evaluation of severity, (3) the patient’s referral at the first consultation with signs of severity, (4) the timing and (5) dosage of antibiotic treatment, (6) the timing and (7) volume of fluid bolus administration, and (8) the clinical reassessment after fluid bolus. Main Outcomes and Measures Two experts assessed the quality of care before death or PICU admission as optimal, possibly suboptimal, or certainly suboptimal. The consequences and determinants of certainly suboptimal care were identified with multinomial logistic regression and generalized linear mixed models. Results Of the 259 children included (median [IQR] age, 24 [6-66] months; 143 boys [55.2%]), 27 (10.4%) died, and 25 (9.6%) had severe sequelae at PICU discharge. The quality of care was certainly suboptimal in 89 cases (34.4%). Suboptimal care was more frequent in children with sequelae (adjusted odds ratio [aOR], 5.61; 95% CI, 1.19-26.36) and less frequent in children who died (aOR, 0.16; 95% CI, 0.04-0.65) vs those surviving without sequelae. Factors independently associated with suboptimal care were age younger than 5 years (aOR, 3.15; 95% CI, 1.25-7.90), diagnosis of sepsis with no source (aOR, 5.77; 95% CI, 1.64-20.30) or meningitis (aOR, 3.39; 95% CI, 1.15-9.96) vs other severe infections, and care by a primary care physician (aOR, 3.22; 95% CI, 1.17-8.88) vs a pediatric hospital service. Conclusions and Relevance This study found that suboptimal care is frequent in the initial management of COSBI and is associated with severe sequelae. The paradoxical association with reduced risk of death may be explained by an insufficient adjustment on bacterial or host intrinsic factors. Management could be optimized by improving the quality of primary care, especially for young children.