If I remember correctly, Ouranos fathered Chronos. Chronos killed Ouranos to take his place as king of the gods. Afraid his kids would do the same to him, Chronos ate them (these included Poseidon and Hades). Then Zeus fed him the rock and made him vomit out all his siblings.

So all together, that accounts for Jupiter, Saturn, Neptune, Uranus, and Pluto.