Wet cough is a common feature of many disease processes affecting children. Our aim was to examine the relationships between cough nature, lower airway infection (bacterial, viral, and viral-bacterial) and severity of neutrophilic airway inflammation. We hypothesized that viral-bacterial co-infection of the lower airway would be associated with wet cough and heightened neutrophilic airway inflammation. We prospectively recruited 232 children undergoing elective flexible bronchoscopy. Participants were grouped using a cough nature symptom-based approach, into wet, dry or no cough groups. Broncho-alveolar lavage (BAL) and clinical data, including presence, nature, and duration of cough and key demographic factors, were collected. Children with wet cough (n = 143) were more likely to have lower airway bacterial infection (OR 2.6, P = 0.001), viral infection (OR 2.04, P = 0.045) and viral-bacterial co-infection (OR 2.65, P = 0.042) compared to those without wet cough. Wet cough was associated with heightened airway neutrophilia (median 19%) as compared to dry or no cough. Viral-bacterial co-infection was associated with the highest median %neutrophils (33.5%) compared to bacteria only, virus/es only and no infection (20%, 18%, and 6%, respectively, P < 0.0001). Children with wet cough had higher rates of lower airway infection with bacteria and viruses. Maximal neutrophilic airway inflammation was seen in those with viral-bacterial co-infection. Cough nature may be a useful indicator of infection and inflammation of the lower airways in children.