Which of the following signs indicates right-sided heart failure in a pediatric patient?

The presence of ascites is a significant indicator of right-sided heart failure in a pediatric patient. Right-sided heart failure can lead to increased pressure in the venous system, which causes fluid to seep out of the blood vessels into the surrounding tissue and cavities, including the abdominal cavity. This fluid accumulation manifests as ascites, which is characterized by abdominal distension and can sometimes be accompanied by discomfort in the child.

While signs like grunting and nasal flaring are often associated with respiratory distress and can indicate other underlying issues, they do not specifically point to heart failure. Clubbing is associated with chronic hypoxia and certain lung diseases but is not directly related to heart failure itself. Therefore, observing ascites serves as a clear and direct sign of right-sided heart failure in pediatric patients, indicating the cardiovascular system's inability to manage venous return effectively.