Which symptom in children with headaches requires immediate evaluation for serious underlying conditions?

The presence of projectile vomiting accompanying a headache in children is a significant symptom that necessitates immediate evaluation for potential serious underlying conditions. Projectile vomiting can indicate increased intracranial pressure, which may be due to various causes such as tumors, meningitis, or other central nervous system issues. This symptom raises red flags in a clinical assessment, suggesting that further investigation is critical to rule out life-threatening conditions.

In contrast, headaches after exercise, those associated with sinus congestion, and occasional headaches relieved by hydration typically do not imply an immediate risk of serious pathology. While they may warrant further evaluation depending on the context, they are generally not considered urgent signs that demand prompt medical attention in the same way projectile vomiting does.