The birth of the monstrous baby, who made Uranus unsatisfied. So he dropped the baby in the pit under the earth. Gaea was upset of how Cronus didn't save his brother.
GO SAVE YOUR BROTHER
Cronus was afraid that one of his children will raise up against him. He kept the power and prophecy to be sure his prediction is true or not .Cronus will then have to eat his kids to escape the fate.
What if my child raise up against me , like I have to my father.
Rhea was heartbroken of how Cronus ate their child accept Zeus .She took Zeus and replace him with crave up stone that look like him. Then she gave Cronus the stone one for him to eat with him noticing.
Rhea would protect Zeus once he grow up to finally get his brothers and sisters . Until then Cronus must not know that he swallow a stone instead of Zeus. Rhea love and cherish him .
Grown to manhood ,Zeus hoped he would reunited with his brothers and sisters .Zeus was hid from Cronus so Cronus would eat him like his brothers and sisters. Rhea would keep him some where he would be feed ,protected , and educated.
When Zeus grow up , he was ready to rise up against his father and get he brothers and sisters back. The goddess Metis helped him,by getting him the potion which will give back the childrens that Cronus swallowed . Zeus was now the supreme god and then he banish his father from his kingdom.