Which group of individuals should avoid taking aspirin due to potential risks?

The recommendation for children with fever to avoid aspirin is based on the association between aspirin use in this age group and the development of Reye's syndrome. Reye's syndrome is a rare but serious condition that can cause liver and brain damage and can occur following the administration of aspirin during viral infections, particularly influenza or chickenpox. This risk is significant enough that health authorities strongly advise against the use of aspirin in children and teenagers who are experiencing fever or viral illnesses.

In contrast, the other groups mentioned do not have the same level of concern regarding aspirin. Active athletes may take aspirin for pain relief or anti-inflammatory purposes, pregnant women have specific guidelines that vary based on their health needs, and individuals with hypertension may require careful monitoring of their aspirin intake due to its potential effects on blood pressure but are not outright contraindicated. Therefore, the primary concern with aspirin use is specifically highlighted in the context of children with fever, making this the correct answer.