Viral Infection (e.g., Upper Respiratory Tract Infection): This is the most common cause of lymphadenopathy in children, often presenting with symptoms such as fever, sore throat, and runny nose. The lymphadenopathy is usually self-limiting and resolves with the resolution of the viral infection.

Bacterial Infections (e.g., Strep Throat, Skin Infections): Bacterial infections can cause lymphadenopathy, especially if the infection is localized near the affected lymph nodes. Symptoms may include fever, localized pain or swelling, and sometimes a rash.
Reactive Lymphadenopathy: This condition occurs in response to a variety of stimuli, including infections, vaccinations, or other inflammatory processes. It is characterized by lymph node enlargement without a specific identifiable cause.
Allergic Reactions: Allergies can sometimes cause lymphadenopathy, particularly if there is an allergic reaction to an insect bite, medication, or certain foods.

Lymphoma: Although rare in children, lymphoma is a critical diagnosis not to miss. It can present with persistent, painless lymphadenopathy, often accompanied by systemic symptoms such as weight loss, fever, and night sweats.
Tuberculosis (TB): TB is another important diagnosis to consider, especially in areas where TB is prevalent or in children who have been exposed to someone with TB. Symptoms can include chronic cough, weight loss, fever, and lymphadenopathy.
HIV Infection: Children with HIV can present with lymphadenopathy among other symptoms. Early diagnosis is crucial for the management and prognosis of HIV infection.

Autoimmune Disorders (e.g., Juvenile Idiopathic Arthritis, Systemic Lupus Erythematosus): These conditions can cause lymphadenopathy as part of their systemic manifestations. They are less common but should be considered in the differential diagnosis, especially if other systemic symptoms are present.
Malignancies (e.g., Neuroblastoma, Leukemia): While rare, other malignancies can also cause lymphadenopathy in children. Neuroblastoma, for example, can present with lymphadenopathy, abdominal mass, and sometimes neurological symptoms.
Cat-Scratch Disease: Caused by Bartonella henselae, this infection can lead to lymphadenopathy, usually following a cat scratch or bite. It is characterized by a papule or pustule at the site of the scratch, followed by lymph node enlargement.