Acute Dystonic Reaction: This condition is characterized by sudden onset of involuntary, sustained, and often painful muscle contractions leading to abnormal postures. It can be triggered by various factors including medications, and the involvement of the upper and lower limb along with speech abnormality could suggest a dystonic reaction, possibly secondary to another condition or medication.

Chorea: This is a neurological disorder characterized by involuntary, unpredictable body movements. Chorea can be a manifestation of various conditions, including Sydenham's chorea, which is associated with rheumatic fever and can present with sudden onset of involuntary movements and sometimes speech disturbances.
Tourette Syndrome: Although typically presenting with a combination of chronic vocal and motor tics, the sudden onset of involuntary movements and speech abnormalities could be considered in the differential, especially if there's a history of similar episodes or a family history of the condition.
Hemiballismus: A rare movement disorder characterized by involuntary, violent, and large-amplitude movements of the proximal part of the limbs, often due to a lesion in the subthalamic nucleus. The sudden onset and unilateral involvement could fit this diagnosis.

Stroke or Cerebrovascular Accident (CVA): Although less common in children, a stroke can present with sudden onset of focal neurological deficits, including involuntary movements and speech abnormalities. It is crucial to consider and rule out this diagnosis due to its severe implications and the need for immediate intervention.
Intracranial Infections (e.g., Encephalitis, Meningitis): These conditions can present with a wide range of neurological symptoms, including sudden onset of involuntary movements and speech disturbances, and require prompt diagnosis and treatment to prevent serious complications.
Metabolic Disorders: Certain metabolic disorders can lead to acute neurological presentations, including involuntary movements. Conditions like Wilson's disease or disorders of amino acid metabolism can have neurological manifestations and are important not to miss.

Moebius Syndrome: A rare neurological disorder characterized by facial paralysis and impaired eye movements, which can sometimes be associated with limb abnormalities. However, it typically presents at birth or early infancy.
Rasmussen's Encephalitis: A rare inflammatory neurological disease, characterized by frequent and severe seizures, loss of motor skills, and speech, often with a progressive course. The involvement of one side of the body could fit, but the disease's progression and other symptoms would be key to this diagnosis.
Sydenham's Chorea with Hemichorea: In some cases, Sydenham's chorea can present unilaterally (hemichorea), which might fit the description of involuntary movements in one side of the body, along with speech abnormalities.