Ptosis: This condition, characterized by the drooping of one eyelid, is a common cause of unequal eye opening in children. It can be congenital or acquired due to various reasons such as weakness of the levator palpebrae superioris muscle, nerve supply issues, or mechanical problems.

Amblyopia: Also known as lazy eye, this condition can lead to unequal vision and potentially affect eye opening due to the brain favoring one eye over the other. However, it's more about vision than physical eye opening.
Strabismus: A condition where the eyes are misaligned, which can cause the appearance of unequal eye opening due to the deviation of one eye.
Hemifacial Spasm or Weakness: Conditions affecting the facial muscles can lead to uneven facial expressions, including eye opening.

Third Cranial Nerve (Oculomotor Nerve) Palsy: This can cause ptosis, among other symptoms like outward and downward deviation of the eye. It's crucial to identify as it can be a sign of a serious underlying condition such as an aneurysm or increased intracranial pressure.
Myasthenia Gravis: An autoimmune disorder that can cause fluctuating muscle weakness, including the muscles controlling eye movements, leading to unequal eye opening.
Stroke or Cerebrovascular Accident: Although rare in children, a stroke can cause sudden onset of unequal eye opening among other neurological deficits.

Congenital Syphilis: Can cause a variety of eye abnormalities, including unequal pupil sizes or eye openings.
Duane Syndrome: A rare congenital disorder that affects the extraocular muscles, leading to limited eye movement and potentially the appearance of unequal eye opening.
Moebius Syndrome: A rare neurological disorder characterized by facial paralysis and impaired eye movements, which could result in unequal eye opening.