Final answer:
The nurse should stress to the parents of an 18-month-old child who underwent surgical repair of hypospadias to avoid tub baths until the surgical site heals and to encourage frequent diaper changes.
Step-by-step explanation:
The postoperative nursing care measure that the nurse should stress to the parents of an 18-month-old child who underwent surgical repair of hypospadias is to avoid tub baths until the surgical site heals. This is important because immersing the surgical site in water can increase the risk of infection and delay healing. Instead, the parents should clean the surgical area gently with warm water and soap, and then pat it dry with a clean towel.
Additionally, the nurse should also stress the importance of encouraging frequent diaper changes. Keeping the diaper area clean and dry helps prevent infection and promotes healing. The parents should change the child's diaper as soon as it becomes soiled or wet. They should also apply a thin layer of petroleum jelly or diaper cream to protect the surgical area from irritation.
The other options mentioned in the question, such as immobilizing the surgical site and administering pain medication as needed, may be necessary depending on the specific surgical procedure and the child's condition. However, the nurse should prioritize educating the parents about tub bath avoidance and frequent diaper changes as these measures directly impact the care of the surgical site.