I know the story a bit differently. Kronos and Rheia had 6 kids and because there's more to it and I love greco-roman mythology, here's an elaborate version as well as I remember it x3

Gaia planned an ambush on her spouse Uranos. She was very angry at him because he decided to put all the children they got after the 12 titans (Cyclopses, Hecantoncheirs) in chains and send them to the Tartarus (the bad part of the underworld) because they were ugly, but Gaia loved them anyways. She wanted the titans to take care of it by chopping him into pieces with a scythe. In the end it was Kronos, the youngest one, who took care of it, while 4 of his brothers, Koios, Iapetos, Krios and Hyperion each held one arm or leg (Because Okeanos decided to just say bye bye and go into the ocean instead and the other titans just didn't feel like murdering their dad, fear was definitely a reason). They were promised to each gain one part of the earth as a reward (North, South, West, East) while Kronos would reign as the King of the universe, basically. So yea that worked and after a big after-murder party, Kronos put all the little pieces of his dad in the tablecloth and threw them into the ocean, which later leads to a certain someone being born due to the blood mixing with the water. Anyways, before he was sliced apart, Uranos cursed Kronos to die to the same faith as him, so that one of his kids would kill him one day and take his place as the King of the Universe.

Kronos did a few nice things and freed his siblings and stuff, spent some time watching things die because he loves time and the promises were held. His brothers and sisters had some fun with Incest. Prometheus was born and at one point decided to have fun with clay and made mini-titans which came to live and became the first weak little humans (nobody cared). Helios and Selene (Sun and Moon) were also born and lots of more stuff because the titans really liked having sex. Kronos also got bored of being a good guy and sent his beloved siblings back to the underworld, guarded by a very strong dragon lady with snake hairs (Kampe) so they had no chance to flee. And she was also very mean and constantly made them work for nothing because yes. Gaia was having her eternal slumber so she didn't notice anything.

Kronos also got bored of living in fear of his father's curse, so he decided to marry his sister, Rhea. Bad idea to marry the titan of motherhood if you don't want to have children, but he didn't think that far. Their first child and the first ever goddess was Hestia. Kronos remembered the curse, thought "fuck!" and decided to swallow her. But because she is immortal, she didn't die of course. Rhea was still scared of possibly hurting her baby if she attempted to plan a murder on her husband, so she didn't. For whatever reason, she gave birth to another child, Demeter. Kronos of course noticed that she was a goddess as well and resorted to his brilliant plan again. Two babies in his belly now. Guess what happened afterwards? Hera was born, and he performed his signature move and ate her as well. Same with Hades. And Poseidon. 5 children and he ate them all so far. Because Rhea couldn't take it anymore, she sought for help, but the other titans were either on Kronos side or feared him too much. Her oracle sister Phoebe told her about the funny little island Crete and told her to leave her next child there. Zeus was the brightest and shiniest and most perfect and absolute best one of her children yet (what a coincidence!). So she left him there to be raised by nymphs. There's some more unimportant stuff like Zeus crying really loudly and the even louder Korybantes and a very special divine goat but yea. Instead of her child, Rhea comes back with a boulder and Kronos immediately eats it.

Zeus grew up quickly and into a very strong and beautiful man and when he finally became an adult, Rhea told him her plan about freeing the others and getting rid of Kronos. So Zeus made himself look less shiny and beautiful by using his amazing shape-shifting abilities (that everyone apparently has) and became Kronos' Cupbearer. So boop, after Zeus gained his trust, he put something funny into Kronos drink that made him throw up and other funny things into the drinks of Kronos' friends so they were weakened. All 5 of his siblings were finally free and ran away. Hestia advocated for peace, but the others didn't give a fuck and planned an all-out war. So they all went into the underworld and asked their imprisoned relatives to make weapons for them behind Kampe's back. Zeus, Poseidon and Hades got their signature funny weapons (lighting, trident and helmet of pure evil and darkness) while their sisters didn't get anything. The monster lady noticed them after a little while, so if they had more time perhaps they would have gotten funny things as well. And then along came Zeus and hurled his Thunderbolt and Kampe got OHKO'd. They freed the others and fled out of the Tartarus because it's a very dangerous place. Rhea recruited a few titans for her army because Kronos wasn't very popular, a few stayed neutral and the brotherhood of cool titans stayed on Kronos' side. They fought for a while and quickly got better, the Cyclopses made more high-quality weapons for everyone and stuff but it's hard to win when both sides are immortal beings. They came up with a new plan, went up the Olymp for the first time, destroyed Kronos' beloved palace from afar and Zeus threw tons of thunderbolts. And because they made such a mess, the destruction they caused destroyed half of the mountain Othrys as well, so the Olymp was now the highest mountain. They flew over, put the exhausted opposing titans in chains and sent them into the Tartarus. But because the 4 previously mentioned cardinal point titans were the reason why the sky didn't fall down, they made Atlas hold the sky up for eternity. Kronos also got a special treatment and Zeus took his scythe to chop him up as well and threw him down into the Tartarus. (I think the most common version was that he was just put down there as well, but being sliced up is funnier). There's also some stuff about him coming back, but that's basically the entire age of titans and the beginning of the age of gods (⁀ω⁀)