Minor Head Injury: Given the age of the child and the height of the fall, a minor head injury is the most likely diagnosis. The child's skull is still relatively soft and pliable, and falls from this height are common in this age group, often resulting in minor injuries.

Scalp Hematoma: A fall onto the back of the head can cause a scalp hematoma, which is a collection of blood outside of blood vessels, often due to a break in the blood vessels.
Linear Skull Fracture: Although less common, a linear skull fracture is possible, especially if the child landed directly on a hard surface.
Concussion: A mild traumatic brain injury, or concussion, could occur from this type of fall, especially if there was significant impact to the head.

Subdural Hematoma: This is a serious condition where blood collects on the brain's surface beneath its outer covering, often due to severe head injuries. It's crucial to identify this condition promptly due to its potential for severe consequences, including death.
Epidural Hematoma: Another serious condition where blood accumulates between the skull and the dura mater (the outermost meningeal layer covering the brain), which can lead to increased intracranial pressure and potentially fatal outcomes if not treated immediately.
Spinal Injury: Although less likely, a fall from this height could potentially cause a spinal injury, especially if the child landed in an awkward position or if there was a pre-existing condition affecting the spine.

Depressed Skull Fracture: This type of fracture, where part of the skull is sunken in from the trauma, is less common in falls from low heights but could occur if the child's head struck a sharp or pointed object.
Basilar Skull Fracture: A fracture at the base of the skull, which is rare but can be associated with significant morbidity and mortality, especially if it involves structures like the cranial nerves or major blood vessels.