Final answer:
The narrowest part of the airway before the age of 10 is the craniopharyngeal or subglottic region. This region is prone to obstruction in young children from small objects or during asthma attacks. As a child grows, the airway's narrowest part transitions to the trachea.
Step-by-step explanation:
Before the age of 10, the narrowest part of the airway is typically the craniopharyngeal or subglottic region, which is located below the vocal cords at the bottom of the larynx. In young children, this area is the narrowest section of the airway and thus, is the most common site for obstruction. Obstruction of the airway in young children often results from small objects, foods like bananas and marshmallows, or mucus during an asthma attack. The craniopharyngeal or subglottic regions are smaller in diameter compared to the width of the trachea, which is about 2.5 cm (1 in.) wide, and it is not until later in childhood that the narrowest part of the airway shifts to the trachea.