What is the most likely diagnosis for a child under 3 years old presenting with inspiratory stridor?

When considering a diagnosis for a child under 3 years old presenting with inspiratory stridor, croup is the most likely condition. Croup, also known as laryngotracheobronchitis, is a common viral infection in young children, typically caused by the parainfluenza virus. It is characterized by swelling in the upper airways, leading to a distinctive "barking" cough and inspiratory stridor due to airway obstruction.

The age of the child is significant since croup most commonly affects children in this age group, especially those between 6 months and 3 years. The presence of stridor in combination with other symptoms such as cough and hoarseness further reinforces the diagnosis of croup, as these signs are typical indicators of the condition.

In contrast, bacterial tracheitis, while it can also present with stridor, is less common and usually occurs in older children or after a bout of viral illness. Epiglottitis, although it presents with stridor and is a serious condition, has become less common due to vaccination against Haemophilus influenzae type b (Hib) and typically presents with acute onset fever, drooling, and difficulty swallowing (dysphagia). Asthma