Cat scratch disease: This is a common cause of axillary lymphadenopathy in children, typically presenting with a history of cat scratch or exposure, followed by the development of a painful axillary lymph node.

Infectious mononucleosis: Caused by Epstein-Barr virus, it can lead to lymphadenopathy, including axillary nodes, along with fever, sore throat, and fatigue.
Streptococcal or staphylococcal infections: Bacterial infections such as impetigo, folliculitis, or abscesses in the arm or chest area can cause axillary lymphadenitis.
Viral upper respiratory infections: Common colds or flu can sometimes cause lymph node enlargement and pain, including in the axilla.

Lymphoma: Although rare, lymphomas such as Hodgkin lymphoma or non-Hodgkin lymphoma can present with lymphadenopathy, including axillary nodes, and are critical to diagnose early.
Tuberculosis: TB can cause lymphadenitis, and axillary nodes can be involved. It's particularly important to consider in children who have been exposed to TB or have risk factors.
Sarcoma (e.g., rhabdomyosarcoma): Soft tissue sarcomas can present with a mass or pain in the axillary region, including involvement of the lymph nodes.

Leukemia: Certain types of leukemia can cause lymphadenopathy, but this is less common as a presenting symptom compared to other signs like anemia, thrombocytopenia, or blasts on a blood smear.
Kawasaki disease: This condition can cause lymphadenopathy, but it's more commonly associated with other symptoms like fever, rash, conjunctivitis, and changes to the lips and oral cavity.
Brucellosis: A zoonotic infection that can cause lymphadenitis among other symptoms, but it's rare and typically associated with specific exposures (e.g., to infected animals or their products).