Level 1: Causes of baby\’s cough and runny nose. Baby\’s cough and runny nose is a common symptom, which may be caused by colds, allergies, tracheitis, bronchitis, etc. Colds are the most common cause, and since children\’s immune systems are not fully developed, they are more susceptible to bacteria and viruses. Allergies can also cause coughing and runny noses in babies, usually due to allergies to certain foods or irritants in the environment. Tracheitis and bronchitis may be caused by air pollution or household environment