What is a contraindication for using Aspirin in children?

Aspirin use in children carries a significant risk, particularly due to the potential development of Reye's syndrome, a rare but serious condition that can cause swelling in the liver and brain. This syndrome has been associated with the use of aspirin to treat viral infections or fever in children and adolescents, especially those under the age of 16. Therefore, age under 16 years serves as a strict contraindication for administering aspirin to this population.

The other options do not directly relate to the contraindication for aspirin use in children. Increased anxiety and a history of fever may influence treatment decisions but are not absolute barriers to the use of aspirin. Similarly, while a history of headaches might prompt a clinician to seek alternative treatments or consider the underlying cause, it does not represent a specific contraindication. Thus, the correct selection indicates a clear age-related restriction grounded in safety considerations.