Croup: This is the most common cause of a barking cough and stridor in a child of this age group. Croup, or laryngotracheobronchitis, is an infection of the upper airway that leads to inflammation and narrowing of the trachea, resulting in the characteristic barking cough and stridor. The fact that the child has normal oxygen levels is consistent with a mild to moderate case of croup.

Epiglottitis: Although less common than croup and typically presenting with more severe symptoms, epiglottitis is an infection of the epiglottis that can cause stridor and a muffled voice. However, it usually presents with significant distress, fever, and often decreased oxygen saturation, which is not mentioned here.
Foreign Body Aspiration: This can cause sudden onset of stridor and cough, especially if the object is lodged in the trachea. The presentation can vary depending on the location and size of the foreign body.
Tracheitis: Bacterial tracheitis can present similarly to croup but often with higher fever and more toxic appearance. It's less common but should be considered, especially if the child does not respond to croup treatment.

Anaphylaxis: Although rare, anaphylaxis can cause stridor due to upper airway edema. It's a life-threatening condition that requires immediate recognition and treatment. Symptoms can include widespread hives, itching, swelling, stomach cramps, diarrhea, rapid heartbeat, and a fall in blood pressure.
Retropharyngeal Abscess: This is a serious infection that can cause stridor due to compression of the airway. It's more common in younger children and often presents with neck stiffness, fever, and difficulty swallowing.
Angioedema: Similar to anaphylaxis, angioedema can cause upper airway obstruction leading to stridor. It can be hereditary or acquired and may not always have the typical allergic symptoms.

Subglottic Stenosis: A congenital or acquired narrowing of the subglottic airway can cause stridor. It's less common and might not present with a barking cough.
Laryngomalacia: This is a congenital condition where the tissues of the larynx are soft and floppy, causing partial airway obstruction when a child breathes in. It's the most common cause of stridor in infants but less likely to present for the first time at the age of 2.
Vocal Cord Paralysis: This can cause stridor due to the inability of the vocal cords to move properly. It's rare in children without a history of trauma, surgery, or neurological conditions.