Viral upper respiratory tract infection (URTI): This is the most common cause of cough in infants, often due to viruses such as rhinovirus, coronavirus, or respiratory syncytial virus (RSV). The age of the child and the presence of a cough without other alarming symptoms make this the most likely diagnosis.

Asthma or reactive airway disease: Although less common in infants, asthma can present with cough, especially if there's a family history or if the cough is persistent and worsens with respiratory infections.
Allergic rhinitis: Allergies can cause chronic cough in infants, especially if they are exposed to allergens like dust mites, pet dander, or pollen.
Gastroesophageal reflux disease (GERD): GERD can cause cough in infants due to the reflux of stomach contents into the esophagus, irritating the throat and airways.

Pneumonia: Bacterial pneumonia is a serious condition that requires prompt antibiotic treatment. Symptoms can include cough, fever, and difficulty breathing.
Pertussis (Whooping Cough): Although vaccination is common, pertussis can still occur, especially in areas with low vaccination rates. It's characterized by a distinctive whooping sound during coughing fits.
Foreign body aspiration: This is an emergency situation where an object is inhaled into the airways, causing coughing, choking, or difficulty breathing.
Congenital heart disease: Certain heart defects can lead to respiratory symptoms, including cough, due to pulmonary congestion.

Cystic fibrosis: A genetic disorder that affects the lungs, pancreas, and other organs, causing persistent cough, among other symptoms.
Primary ciliary dyskinesia: A rare genetic disorder affecting the cilia in the respiratory tract, leading to chronic respiratory infections and cough.
Tuberculosis (TB): Although rare in infants in many parts of the world, TB can cause cough and requires specific treatment to prevent long-term complications and transmission to others.