Final answer:
The nurse should recognize increased urine output as a sign of diabetes insipidus in a child after a head injury, which is characterized by the inability of the kidneys to retain water due to inadequate ADH.
Step-by-step explanation:
A nurse caring for a 10-year-old child following a head injury should identify increased urine output as an indication that the child is developing diabetes insipidus. This condition is characterized by a chronic underproduction of the antidiuretic hormone (ADH) or a mutation in the ADH receptor, which results in the inability of the kidneys to retain water, causing excessive urination and increased thirst. The excess water taken in is not retained by the body and is lost again through urine, needing to be continually consumed to maintain hydration. Diabetes insipidus is therefore most likely indicated by polyuria (increased urine output), and it is distinct from diabetes mellitus, which also causes polyuria but additionally, the urine contains high levels of glucose.