Streptococcal Pharyngitis: This is the most likely diagnosis given the presentation of strep throat, which is typically characterized by sudden onset of sore throat, fever, and swollen lymph nodes. The diagnosis can be confirmed with a rapid strep test or throat culture.

Viral Pharyngitis: Many cases of sore throat in children are caused by viral infections, which can present similarly to strep throat but typically have a more gradual onset and may be accompanied by other viral symptoms such as cough or runny nose.
Infectious Mononucleosis: Caused by the Epstein-Barr virus, this condition can also present with sore throat, fever, and swollen lymph nodes, although it often includes additional symptoms like fatigue and hepatosplenomegaly.

Lemierre's Syndrome: A rare but potentially life-threatening condition that starts with pharyngitis and can progress to jugular vein thrombosis and metastatic infections. Early recognition and treatment are crucial.
Retropharyngeal Abscess: A serious infection in the tissues at the back of the throat, which can cause severe throat pain, difficulty swallowing, and breathing problems. Prompt diagnosis and treatment, often surgical, are necessary to prevent complications.

Diphtheria: A bacterial infection affecting the throat and upper respiratory system, characterized by a thick, grey membrane covering the tonsils and throat. It's rare in areas with high vaccination coverage but can be deadly if not treated.
Peritonsillar Abscess: A collection of pus behind the tonsils, which can cause severe throat pain, difficulty swallowing, and fever. While not as immediately life-threatening as some other conditions, it requires prompt medical attention for drainage and antibiotic treatment.