What over-the-counter medicine can i use for ringworm on the scalp on a 7 year old child?

Nizoral (ketoconazole) shampoo: Nizoral (ketoconazole) shampoo 1% is available over the counter. It's an antifungal shampoo and may help some. However, 2% is prescription, and if it's really in the hair, you'll need an oral medicine too along with the Nizoral (ketoconazole) shampoo.

Won't fix it: When the scalp is invaded by the germ of ringworm it gets into the root system of the hair, far too deep for superficial creams or lotions to kill it all. They can attack the exposed fungus, but the root associated germ just replaces what is affected by the creams. See your doc for proper diagnosis. This commonly takes a month or more of oral anti-fungal meds.