Up to 2 percent of babies are born with small, brown-to-black moles, which doctors call nevi. Large ones -- generally classified as bigger than 2 inches in diameter at birth -- occur in less than one out of 100,000 babies. Moles can appear anywhere on the body, tend to grow along with a child, and generally don't go away.
The risk of a small mole becoming cancerous is minimal. There's about a 4 percent chance that a large mole will convert over time, says Dr. Friedlander.
Small moles are generally not a concern. Large ones, which can wrap around the front and back of the body, may be surgically removed. But this often requires multiple procedures, including expanding or grafting skin to cover the excision site.