**Core Concept**
Subdural hematoma is a type of traumatic brain injury that occurs when blood accumulates in the space between the dura mater and the arachnoid membrane surrounding the brain. In children, subdural hematomas are often associated with non-accidental head trauma, such as shaken baby syndrome or child abuse.

**Why the Correct Answer is Right**
Subdural hematoma is not typically a sign of accidental injury in a child. This is because accidental injuries, such as falls or minor bumps, usually result in more superficial injuries like abrasions or bruises. In contrast, subdural hematomas are often indicative of more severe and intentional trauma, such as child abuse or shaken baby syndrome. The mechanism of injury involves a sudden deceleration or acceleration of the head, which causes the bridging veins between the brain and the dura mater to tear, leading to bleeding into the subdural space.

**Why Each Wrong Option is Incorrect**
**Option B:** Abrasion on the knees is a common sign of accidental injury in children, as it can occur from falls or minor scrapes.
**Option C:** Swelling in the occiput can be a sign of accidental injury, such as a fall onto the back of the head, but it is not as specific or concerning as subdural hematoma.
**Option D:** Bleeding from the nose can occur from a variety of causes, including accidental injuries, and is not a reliable indicator of non-accidental trauma.

**Clinical Pearl / High-Yield Fact**
In children, it's essential to consider the possibility of non-accidental trauma when evaluating signs of head injury, especially if there are multiple injuries or inconsistent explanations for the mechanism of injury. The presence of a subdural hematoma should prompt a thorough investigation into the child's medical and social history.

✓ Correct Answer: A. Subdural hematoma