Final answer:
The child with pertussis should be kept at home until the catarrhal stage has passed because the disease is most communicable in this stage.
Step-by-step explanation:
Pertussis is most communicable during the catarrhal stage. This is the initial stage of the disease, when the child may experience mild symptoms such as nasal congestion, runny nose, and a low-grade fever. However, it is important for the child with pertussis to stay at home until this stage has passed to prevent the spread of the highly contagious disease.