Opioid intoxication or exposure: This is a common cause of pinpoint pupils in children, and given the age, accidental ingestion of opioids or exposure to opioid-containing substances is a significant concern.

Pontine glioma: Although less common, tumors in the pons area of the brain can cause pinpoint pupils due to damage to the pons, which affects the pupillary reflex pathways.
Horner's syndrome: This condition, characterized by a triad of ptosis, miosis (pinpoint pupil), and anhidrosis, can be caused by various factors including congenital conditions, trauma, or infections affecting the sympathetic nervous system.
Congenital conditions: Certain congenital conditions can lead to small pupils, including congenital Horner's syndrome or other neurodevelopmental disorders.

Brainstem injury or hemorrhage: Any injury or bleeding in the brainstem can lead to pinpoint pupils and is a medical emergency requiring immediate attention.
Meningitis or encephalitis: Infections of the meninges or brain can cause changes in pupil size, among other symptoms, and are critical to diagnose and treat promptly.
Hydrocephalus: Increased intracranial pressure due to hydrocephalus can cause changes in pupil size and is a condition that requires urgent medical intervention.

Familial dysautonomia (Riley-Day syndrome): A rare genetic disorder that affects the development of the autonomic nervous system, leading to various symptoms including small pupils.
Argyll Robertson pupils: A condition where pupils constrict when focusing on a near object but do not react to light, often associated with neurosyphilis, which is rare in children but can be congenital.
Mitochondrial disorders: Certain mitochondrial disorders can affect the nervous system and lead to abnormalities in pupil size, though this would be part of a broader spectrum of symptoms.