A 5-year-old child of African descent presents with brown-black pigmentation distributed symmetrically across the gingiva and oral mucosa. There is no associated pain and no history of medication use. What is the most likely diagnosis?

Physiological (racial) pigmentation is the most common cause of oral melanin pigmentation, particularly in individuals of African, Asian, Hispanic, or Mediterranean descent. It presents as symmetrical, bilateral brown to black pigmentation of the attached gingiva, hard palate, tongue, and buccal mucosa. It is asymptomatic, benign, and requires no treatment. In a 5-year-old with no medications and symmetric distribution, this is the most likely diagnosis. Oral melanoma is exceedingly rare in children. Amalgam tattoo typically presents as a localized gray-blue macule near restorations. Addison's disease (adrenal insufficiency) can cause oral pigmentation but typically presents in adults with systemic symptoms.