If your baby has ringworm on his body, he'll have one or more scaly patches, probably between the size of a dime and a quarter. While the patches don't always start out round, by the time they're about half an inch across, they usually form a scaly ring around a smooth center. As the fungus grows, the ring gets larger, but it usually stops growing by the time it's about an inch in diameter. The rash can be dry or moist, and it can appear almost anywhere on the body.
When the fungus affects the scalp, the rash usually has less of a ring-like appearance. Instead, you might notice either patchy, scaly areas or bald spots on your baby's head. You may also see stubs of hair broken off in the middle of the bald spots.
Your baby might also develop an area of inflammation, called a kerion, in response to the fungus. It'll appear as a moist, swollen area on the scalp, with pustules (little pimple-like bumps). This will clear up when you treat your baby's scalp for the ringworm.