Cheek (colloquial/childlike); the soft flesh on either side of the face.
赤ちゃんのほっぺをぷにぷに触った。
I poked the baby's cheek; it was squishy.
冬はほっぺが冷たくなるから、マフラーで隠す。
In winter my cheeks get cold, so I cover them with a scarf.
彼女は照れてほっぺを赤くした。
She blushed and her cheeks turned red.