1. Kronos came to power by cutting off certain parts of his dad, Ouranos, that would ensure Ouranos would not be having any more children. Nice.
2. Winning Bad Father of the Year award, he wanted to get rid of his children in case they stole his power.
3. Ensuring he kept the title, he decided the best way to get rid of his kids was to eat them. Which seems a little extreme.
Fortunately, Rhea, wife of Kronos and mother of the child-flavoured snacks took a stand and fed Kronos a rock when he went to munch on Zeus. Zeus then grew up to lead a revolt against Kronos, and banished him to Tartarus.
The particularly gruesome picture of Kronos here is by Francisco Goya. Although it looks like it could have come out of a modern horror movie, it was painted nearly 200 years ago. Some more of Goya's grisly 'black paintings' can be seen here.