CAP is a major cause of pediatric hospitalization on a global scale, particularly in developing countries where the morbidity and mortality rates remain high. The etiological diagnosis of CAP in children is challenging, particularly for children with severe and high-risk conditions, such as immunodeficiency. This is primarily due to the nonspecific distribution of the causative agent and the limitations of traditional detection methods. As an emerging molecular diagnostic technology, BALF mNGS has been shown to detect the nucleic acid sequences of bacterial, viral, fungal, and atypical pathogens directly from clinical samples. This is attributed to the technology's unbiased, high throughput, and high sensitivity, which significantly improves the detection rate of pathogens. Furthermore, BALF mNGS also improves the detection of mixed infections. This capacity for precise analysis is of significant value, as it facilitates the identification of drug-resistant genes and rare pathogens. Consequently, this enhanced diagnostic capability provides a reliable foundation for the precise treatment of childhood CAP. Nevertheless, its clinical application continues to encounter challenges, including high cost, invasive sampling methods, complex data analysis processes, and insufficient standardization of pre-analytical sample processing. The technical principles, clinical value and optimization strategies of BALF mNGS are systematically reviewed in this paper, with the aim of providing a reference for improving the pathogenetic diagnosis of CAP in children.