There are several factors that may cause dark gums in children, but the most-common reasons include a lack of proper hygiene, plaque and tartar buildup, ethnic background, and hereditary factors. Less-common but more-serious reasons are internal bleeding, dead gum tissue and HIV.
If there are black spots on the gums of babies, they are most likely due to teething, but if it is more generalized and spreading, the child should be checked for internal bleeding. The majority of dark gum cases can be treated by properly brushing and flossing, gargling with mouthwash, and maintaining a healthy diet. If the cause is not found and the coloration is spreading or thickening, it is important to seek immediate medical attention.