Acquired Non-Acute Concomitant Esotropia: This condition is a common cause of new onset strabismus in children, often presenting with esotropia (inward turning of the eyes) and can be associated with headaches due to eye strain. It's a refractive error that can develop in children around this age.

Refractive Error: Uncorrected refractive errors such as hyperopia (farsightedness), myopia (nearsightedness), or astigmatism can cause eye strain leading to headaches and potentially strabismus.
Convergence Insufficiency: A condition where the eyes have difficulty converging or working together, which can cause eye strain, headaches, and sometimes strabismus.
Amblyopia: Although typically identified earlier, amblyopia (lazy eye) can sometimes present later in childhood and may be associated with strabismus and headaches due to vision problems.

Brain Tumor: Although rare, brain tumors such as medulloblastoma or craniopharyngioma can cause increased intracranial pressure leading to headaches and new onset strabismus due to cranial nerve palsies.
Idiopathic Intracranial Hypertension (IIH): Also known as pseudotumor cerebri, this condition can cause increased intracranial pressure, leading to headaches and, occasionally, sixth nerve palsy resulting in strabismus.
Stroke: Pediatric stroke, though uncommon, can present with sudden onset of strabismus and headache among other neurological deficits.

Graves' Disease: Thyroid eye disease associated with Graves' disease can cause strabismus due to orbital inflammation and muscle involvement, but it's less common in children.
Myasthenia Gravis: An autoimmune disorder that can cause fluctuating muscle weakness, including the muscles controlling eye movements, leading to strabismus and potentially headaches.
Orbital Cellulitis or Abscess: Infections in the orbit can cause proptosis, pain, and strabismus, but these are usually accompanied by significant orbital swelling and redness.