Muscle Strain: This is a common condition in children that can occur due to overuse or minor, unreported trauma. The lack of a reported injury does not rule out minor strains that could lead to spasm and pain.

Viral Pharyngitis: Infections such as strep throat can cause neck pain and stiffness due to lymph node enlargement and inflammation.
Torticollis: This condition, characterized by a twisted neck, can be congenital or acquired and may cause significant discomfort and spasm.
Cervical Spondylosis: Though more common in adults, children can also experience cervical spondylosis, especially if there's a family history or early onset of degenerative changes.

Meningitis: Although less likely, meningitis is a life-threatening condition that can present with neck stiffness and pain. Early diagnosis is crucial for effective treatment.
Spinal Epidural Abscess: A rare but serious condition that requires prompt medical attention. Symptoms can include severe neck pain and stiffness.
Rheumatologic Conditions (e.g., Juvenile Idiopathic Arthritis): These conditions can cause neck pain and stiffness among other systemic symptoms.

Klippel-Feil Syndrome: A rare congenital condition characterized by the fusion of any two of the seven cervical vertebrae, which can lead to neck stiffness and limited range of motion.
Cervical Spine Tumors: Tumors such as osteoid osteoma or other benign/malignant growths can cause localized pain and stiffness.
Infectious Spondylitis/Discitis: Infections of the spine that can cause pain, stiffness, and systemic symptoms, often requiring prolonged antibiotic treatment.