Which symptom is most predictive of asthma in young children?

The symptom most predictive of asthma in young children is more than three episodes of wheezing per year. Wheezing is a common respiratory symptom that indicates airflow obstruction in the airways, which is characteristic of asthma. Frequent episodes of wheezing suggest a higher likelihood of underlying airway hyperreactivity and potential diagnosis of asthma, particularly in the context of a child's age.

While a single episode of wheezing may occur in young children due to various factors, it is not specific or predictive of chronic asthma as it could also be triggered by viral infections or other non-asthmatic conditions. Similarly, experiencing respiratory distress after exercise is a concerning sign but is not solely indicative of asthma, as other respiratory issues could also cause this symptom without fulfilling the diagnostic criteria for asthma in children. Daily cough at night can indicate asthma but is not as strong a predictor on its own compared to frequent wheezing episodes, as cough can result from other conditions such as allergies or infections.

In summary, the presence of more than three episodes of wheezing in a year is a clearer indicator of asthma due to the chronic and recurrent nature of this symptom in the disease's typical presentation in young children.