Final answer:
The priority intervention for a child with Kawasaki disease is monitoring for extra heart sounds and low urine output as these can indicate serious heart complications.
Step-by-step explanation:
The priority nursing intervention in the provision of care for a pediatric client diagnosed with Kawasaki disease is C. Monitoring for extra heart sounds and low urine output. Kawasaki disease affects the blood vessels and can lead to heart complications, hence it's critical for nurses to monitor cardiovascular status meticulously. This includes listening for additional heart sounds that may indicate cardiac dysfunction or the development of coronary artery aneurysms, and keeping an eye on urine output as a reflection of the child's circulatory status. Low urine output can be a sign of poor cardiac output and is a serious concern.