Accidental trauma: This is the most likely diagnosis for a toddler head injury, as toddlers are prone to falls and accidents due to their curiosity and lack of coordination. The mechanism of injury is often a fall from a short distance, such as a bed or a chair.

Non-accidental trauma (child abuse): Unfortunately, child abuse is a common cause of head injury in toddlers. Healthcare providers should be vigilant for signs of abuse, such as inconsistent histories, multiple injuries, or injuries that are not consistent with the reported mechanism.
Infection (meningitis or encephalitis): Infections such as meningitis or encephalitis can cause symptoms that mimic a head injury, such as altered mental status, fever, and irritability.
Seizure disorder: Toddlers who experience a seizure may injure their head during the seizure, or the seizure may be caused by a head injury.

Epidural hematoma: This is a life-threatening condition that requires prompt diagnosis and treatment. Toddlers with an epidural hematoma may present with a loss of consciousness, vomiting, and signs of increased intracranial pressure.
Subarachnoid hemorrhage: This is another life-threatening condition that requires prompt diagnosis and treatment. Toddlers with a subarachnoid hemorrhage may present with a sudden loss of consciousness, vomiting, and signs of increased intracranial pressure.
Skull fracture: A skull fracture can be a sign of a more serious injury, such as an epidural hematoma or a subarachnoid hemorrhage.

Arteriovenous malformation (AVM): An AVM is a rare congenital condition that can cause a head injury or bleeding in the brain.
Tumor: A brain tumor is a rare cause of head injury in toddlers, but it should be considered in the differential diagnosis, especially if the child has a history of developmental delays or other neurological symptoms.
Vascular disorders (e.g., moyamoya disease): These are rare conditions that can cause a head injury or bleeding in the brain.