While different peoples have varying tales, some elements stay the same. Trying to understand the unfathomable is a common goal of all people. We create stories as an explanation to fill in the unknown. Over time, a set narrative is established to explain the times before history: mythologies.
Ouranos feared that his children would overtake him. He tried to prevent that by forcing his children underground (inside of Gaea). Kronos defeated Ouranos with a sickle.
Kronos castrated his father with a sickle. He feared one of his children would overtake him and he ate all of his offspring.
His wife tricked him into eating a stone instead of his youngest son. Zeus overthrew Kronos with the help of Giants and other allies.