Lymphoblastic Lymphoma: This is a common cause of lymphadenopathy in children, particularly in the jugular and gastric regions. The age of the patient and the location of the lymphadenopathy make this diagnosis highly plausible.

Hodgkin Lymphoma: Although less common in this age group compared to lymphoblastic lymphoma, Hodgkin lymphoma can present with lymphadenopathy in the neck and is a significant consideration.
Non-Hodgkin Lymphoma (other types): Other forms of non-Hodgkin lymphoma, such as Burkitt lymphoma or large cell lymphoma, can also present with lymphadenopathy and should be considered in the differential diagnosis.
Leukemia: Leukemic infiltration can cause lymphadenopathy, and given the age of the patient, acute lymphoblastic leukemia (ALL) is a possibility.

Tuberculosis: Although less likely in some regions, tuberculosis can cause lymphadenopathy and is crucial to diagnose due to its public health implications and the need for specific treatment.
Histoplasmosis or Other Fungal Infections: In endemic areas, histoplasmosis and other fungal infections can cause lymphadenopathy and are critical to diagnose due to their potential severity if left untreated.
Sarcoidosis: Rare in children, but can cause lymphadenopathy and requires specific management.

Langerhans Cell Histiocytosis: A rare disorder that can cause lymphadenopathy among other systemic symptoms.
Kikuchi-Fujimoto Disease: A rare, self-limiting condition that can cause lymphadenopathy, more commonly seen in Asian populations.
Castleman Disease: A rare lymphoproliferative disorder that can present with lymphadenopathy.
Metastatic Disease: Although extremely rare in children, certain malignancies can metastasize to lymph nodes and should be considered in the differential diagnosis, especially if other signs of malignancy are present.