Final answer:
Mongolian spots, or congenital dermal melanocytoses, most commonly occur on the lower back and buttocks of infants. They are harmless and fade over time as the child grows.
Step-by-step explanation:
Congenital dermal melanocytoses, commonly known as Mongolian spots, most commonly occur on the lower back and buttocks of infants. They are characterized by large brown spots on the skin that may be sprinkled with darker specks. These spots are typically harmless and fade over time as the child grows.