In many myths, Zeus's children are Ares, Athena, Aphrodite, Hecate, Hestia, Dionysis, Chiron, and more. They have more kids than I can count. Actually Chiron his father is Kronos so Chiron so,...
Children's is a word that denotes something that belongs to more than one child. There is no such word as childrens' because children is already plural and does not need an 'S' at the end.
Your children and your first cousin's children are second cousins to each other.Your children and your second cousin's children are third cousins to each other.