In Greek mythology, the Titan Cronus (Kronos) — fearing a prophecy that his child would overthrow him — swallowed each of his offspring at birth. His wife Rhea finally tricked him, saving Zeus. The five siblings Zeus later freed (by forcing Cronus to regurgitate them) were:
Together with Zeus, these six became the core Olympian deities who defeated the Titans in the Titanomachy and ruled from Mount Olympus.
Note: The prompt mentions "Zeus and Metis" — Metis was Zeus's first wife (swallowed by Zeus, not Cronus), mother of Athena. The five swallowed by Cronus are the ones listed above.