Cutaneous mastocytosis represents a spectrum of disorders characterized by localized or diffuse accumulation of mast cells within the skin. Solitary mastocytoma is the most frequent variant in children and typically presents during infancy. However, occurrence at atypical anatomical sites may lead to diagnostic uncertainty. We report a case of a two-year-old boy who presented with a single, well-demarcated, reddish-brown nodulo-plaque over the left supra-mammary region. The lesion exhibited a characteristic peau d’orange surface and demonstrated a positive Darier’s sign. There were no associated systemic complaints such as flushing, gastrointestinal disturbances, or syncopal episodes. Histopathological examination revealed dense dermal infiltration by mast cells, which were confirmed by the presence of metachromatic granules on Giemsa staining. The lesion showed significant regression following intralesional triamcinolone therapy. This case highlights the importance of recognizing classical clinical signs in unusual locations and emphasizes the role of clinicopathological correlation in establishing the diagnosis.