Cytomegalovirus (CMV) pneumonitis infections might present mild or severe illnesses and need sophisticated diagnostic tools, so it remains a diagnostic challenge. We reported five infants diagnosed with CMV pneumonitis who were initially and undiagnosed by the pediatrician in secondary private or public health hospitals with no improvement with standard and escalation of antibiotics treatment for bronchopneumonia as the initial diagnoses. As all cases occurred during the COVID-19 pandemic, they proved negative COVID-19 identified by polymerase chain reaction (PCR) SARS-CoV-2. We diagnosed acquired perinatal pneumonitis CMV in all claims based on clinical criteria, imaging studies, CMV serology, and PCR-CMV urinary tests as diagnostic tools. They showed clinical improvement after two weeks of valganciclovir therapy. Other organs' involvement was considered to be evaluated, including brain-evoked response audiometry (BERA) and eye examination. The physician should consider the possibility of CMV pneumonitis, who did not respond to standard and escalation of antibiotics treatment after initial diagnoses of bronchopneumonia.