Final answer:
The diagnosis supported by a solitary purplish lesion on the head that looks like a spongy mass in a newborn child is Hemangioma.
Step-by-step explanation:
The diagnosis supported by a solitary purplish lesion on the head that looks like a spongy mass in a newborn child is Hemangioma. Hemangiomas are benign tumors made up of blood vessels and commonly occur in infants. They can appear as reddish or purplish spongy masses on the skin.