Mistake #1: Eating your children. This is crazy to begin with. Why would someone eat their own children? I suppose when you’re a god, or even a king for that matter, this would stop them from trying to claim your power. However, this is a fantastic way to make enemies in people such as, I don’t know, your wife, the mother of those children you’ve been making meals out of. (Note: This was actually a precaution, Cronus was aware that one of his sons would “kill” him. Nevertheless, he should have know that there’s no getting around the Fates.)
Mistake #2: Underestimating your wife. Rhea, the wife of Cronus, was another Titan. I don’t think it matters if you are a god, you do not want the wrath of a divine woman on you!
Mistake #3: Believing a rock is your son. Rhea hid her and Cronus’s son, Zeus, and fed Cronus a rock instead. How do you mistake a rock for your son?! You should be able to tell the difference with all five of your senses! A rock is much harder than a baby. A rock does not smell like a baby. A rock does not look like baby. A rock does not cry like a baby. And, while I cannot honestly say that I have tried either, I can’t imagine that a rock tastes like a baby!
Mistake #4: Not digesting those kids. Well, I guess you can’t really blame ole Cronus for this one. The gods are immortal, after all. Apparently they can’t die even if they are eaten and sitting in the belly of a Titan for years. This just serves as a reason why Cronus should have disposed of the future Olympians in another, more effective, manner.
After this series of mistakes, Zeus returned and cut his father open, allowing his five siblings, Demeter, Hades, Poseidon, Hera, and Hestia, to escape. Zeus proceeded to banish Cronus and usurp his throne.
If Cronus had not decided to eat his children, and instead chose to nurture them and keep good relations with them, his reign would likely have lasted much longer, probably forever, seeing that he was immortal.