Final answer:
The extrathoracic dead space in children is affected by their age and size, and is generally smaller compared to adults.
Step-by-step explanation:
Compared to adults, the extrathoracic dead space in children is affected by their age and size. Extrathoracic dead space is the portion of dead space that occurs outside of the respiratory system. In children, it is generally smaller compared to adults due to their smaller size and narrower airways. As children grow and develop, their extrathoracic dead space decreases.