Final answer:
An Electroencephalogram (EEG) is the indicated diagnostic test for a child with a single non-febrile seizure and a normal neurological exam, as it helps identify the brain regions involved in the seizure.
Step-by-step explanation:
The appropriate diagnostic test for a child who has had a single non-febrile seizure with a normal neurologic exam is an Electroencephalogram (EEG). An EEG involves placing electrodes on the scalp to record electrical activity in the brain. This test can help to determine which brain regions may have been involved in the seizure. The other options such as Computerized tomography (CT), Magnetic resonance imaging (MRI), and Polysomnography are not the primary tests indicated for a single seizure event without other neurological deficits or concerns.