Bacterial infectious acute pneumonia has long presented a significant barrier to human health and the fast elimination of antibacterial in lung tissue. Engineering nanoformulations that are easily prepared and possess mucoadhesive characteristics for administering antibacterial drugs are crucial for addressing pneumonia and lung injury. This investigation utilized FDA-approved tannic acid (TA) to develop a nanocomplex by cloaking chitosan (CH) to attain prolonged anti-infection efficacy against acute pneumonia. The flash nanocomplexation (FNC) process was employed for developing chitosan-cloaked poly(vinyl alcohol)/TA/N-acetylcysteine (NAC) nanoparticles (CPTN NPs) using NAC as the model drug, relying on non-covalent interactions between the components. The investigation of pneumonia revealed that the robust electrostatic interaction between negatively charged mucin and positively charged chitosan in the trachea facilitated the retention of NAC in the lungs for a minimum of 24 h post-inhalation of CPTN NPs, effectively constraining pneumonia within 3 days. The DPPH values of 97.42 ± 5.1 for CPTN NPs reveal excellent antioxidant ability. The cell viability of NCI-H441 and A549 cells remained above 90% of 100 μg/mL for NAC and CPTN NPs. The antibacterial efficacy of CPTN NPs exhibited a 99.9% reduction compared to the untreated group. The mucoadhesive CPTN NPs, characterized by excellent biocompatibility and produced using a simple and reproducible method, may offer a novel approach to administering CPTN NPs to address acute pediatric pneumonia and lung injury.