Premature thelarche or breast bud: This is a common condition in prepubertal girls, characterized by the early development of breast tissue, which can present as a subareolar mass. It's often a benign condition and a variation of normal development.

Breast cyst or abscess: These can occur in children and present as a mass, though they are less common than in adults. Infection or blockage of the ducts can lead to abscess formation.
Fibroadenoma: A benign tumor of the breast that can occur in adolescents and pre-teens, presenting as a firm, mobile mass.
Accessory breast tissue: Extra breast tissue that can develop along the milk line, which runs from the armpit to the groin, and can sometimes be mistaken for a subareolar mass.

Rhabdomyosarcoma or other soft tissue sarcomas: Although rare, these malignant tumors can present as a mass in the breast area and are critical to diagnose early due to their aggressive nature.
Metastatic disease: Though exceedingly rare in children, certain cancers can metastasize to the breast, emphasizing the importance of a thorough diagnostic workup.
Inflammatory breast cancer: Extremely rare in children but can present with a mass and skin changes, making it crucial not to miss due to its aggressive nature.

Hematoma or vascular malformations: These can present as a mass but are less common in the subareolar region without a history of trauma.
Tuberculosis or other granulomatous infections: Can cause masses in the breast tissue, though this is rare in children and more commonly associated with systemic symptoms.
Phyllodes tumor: A rare tumor of the breast that can be benign, borderline, or malignant, presenting as a rapidly growing mass.