Viral Upper Respiratory Tract Infection (URTI): This is the most common cause of cough and cold in infants, often caused by viruses such as rhinovirus, coronavirus, or respiratory syncytial virus (RSV). The presentation without respiratory distress suggests a mild infection.

Bronchiolitis: Although typically seen in infants under 1 year, especially during RSV season, it can present with cough and sometimes without initial respiratory distress. It's crucial to monitor for signs of worsening.
Allergic Rhinitis: Though less common in infants, exposure to allergens could lead to allergic rhinitis, presenting with cough and cold symptoms.
Gastroesophageal Reflux Disease (GERD): Can cause cough in infants due to the reflux of stomach contents into the esophagus, irritating the throat.

Congenital Heart Disease: Although less likely, undiagnosed congenital heart disease can present with respiratory symptoms due to pulmonary congestion or other complications. It's critical to consider this in the differential due to its severe implications.
Pneumonia: Bacterial pneumonia can initially present with mild symptoms but can rapidly progress, especially in young infants. It's essential to monitor for signs of respiratory distress or failure.
Inborn Errors of Metabolism: Certain metabolic disorders can present with nonspecific symptoms, including respiratory issues. Early diagnosis is crucial for management.

Cystic Fibrosis: A genetic disorder that can lead to recurrent respiratory infections and other complications. Early diagnosis through newborn screening or clinical presentation can significantly impact management.
Primary Ciliary Dyskinesia (Kartagener Syndrome): A rare genetic disorder affecting the cilia, leading to recurrent respiratory infections and other systemic issues.
Foreign Body Aspiration: Although more common in older infants and toddlers, it's a possibility in any age group and can present with sudden onset of cough and respiratory distress.