Urinary Tract Infection (UTI) complications: The recent UTI could have led to lymphadenitis, which is an inflammation of the lymph nodes, often caused by a bacterial infection. This is a common and direct complication that could explain the lymph node enlargement.

Viral infections (e.g., adenovirus, EBV): Viral infections are common in children and can cause lymphadenopathy. Given the age of the patient, viral infections are a plausible cause.
Bacterial infections (e.g., streptococcal, staphylococcal): Besides UTI, other bacterial infections could lead to lymph node enlargement, especially if the infection is localized near the affected lymph nodes.
Reactive lymphadenopathy: This is a condition where lymph nodes become enlarged in response to an infection or inflammation elsewhere in the body, which could be related to the recent UTI or another concurrent infection.

Tuberculosis (TB): Although less common, TB can cause lymphadenopathy and is crucial to diagnose early due to its potential severity and the need for specific treatment.
Lymphoma: While rare in children, lymphoma is a critical diagnosis not to miss, as it requires prompt and specific treatment.
Cat-scratch disease: Caused by Bartonella henselae, this infection can lead to lymphadenopathy, typically after a cat scratch or bite, and is important to consider in children who are around cats.

Histiocytosis: A rare condition where abnormal immune cells accumulate in various parts of the body, including lymph nodes, leading to their enlargement.
Kawasaki disease: An acute febrile illness that can cause lymphadenopathy among other symptoms, although it's more commonly associated with other specific findings like rash, conjunctivitis, and changes to the lips and oral cavity.
Autoimmune disorders (e.g., systemic lupus erythematosus, rheumatoid arthritis): These conditions can cause lymphadenopathy but are rare in young children and typically present with a constellation of other symptoms.