Cronus believes he has taken his first step to greatness here. He has assassinated his own father and with the support of his mother, will rise to be king, but in fact, this is the beginning of the end for him as Uranus curses him with his dieing breath. Now he and all the generations who follow him shall fear their own children, who will one day rise up to usurp their role in the world.
This is a recurring theme in Greek myth, and all goes back to this story, or at least this story was created to explain this fear. Cronus would be tortured by this curse all through his reign, and Zeus himself would take horrible actions in the future, hoping to forestall falling victim to the same fate.