1. To research the current situation of severe infection in children in China, and to investigate the incidence, prognosis and disease burden of severe infection in children in different regions of China. 2. Establish the risk prediction model and diagnosi model of severe infection in children, and verify the accuracy of the model in multi-center; 3. To study the effectiveness and safety of different treatments in real diagnosis and treatment, and to evaluate the efficacy of subgroups under different ages and high risk factors.

1.Children between 0 and 18 years old. 2.Severe pneumonia and/or sepsis.Patients were included who meet the guidline for diagnosis and treatment of community-acquired pneumonia in Children (2019) issued by the National Health Commission of the people's Republic of China and/or who meet the International Guide to the 2020 campaign to Save sepsis: management of septic shock and sepsis-related organ dysfunction in children. 3.notifiable infectious diseases.4.The researcher believes that he is not suitable to participate in other situations in this study.5.Participants in other clinical trials in the same period.

Inclusion Criteria:

1. Children between 0 and 18 years old.
2. Severe pneumonia and/or sepsis.

Exclusion Criteria:

1. notifiable infectious diseases.
2. The researcher believes that he is not suitable to participate in other situations in this study.
3. Participants in other clinical trials in the same period.

All children hospitalized in PICU of Children's Hospital of Fudan University from April 2021 to April 2025