Your cousin's children are your second cousins
second cousins to his cousin's children, you'd be third cousins
You and your first cousin's son are first cousins, once removed.
Your son and your nephew are First Cousins. The children of your nephew and the children of your son are Second Cousins to each other.
your son and your brother's son will be cousins
your son and your brother's son will be cousins
Your children and your first cousin's children are second cousins.
your son and your brother's son will be cousins
Your aunt's child, son or daughter, is your First Cousin. The same is true for your uncle's children.
Two people who have at least one grandparent in common are first cousins. Your son and your stepbrother's son may be first cousins, or may be unrelated. Even if they are unrelated that can call each other first cousins if they get on well together and want to do that.
Your first cousin's son and your children are second cousins to each other. Your second cousin's son and your children are third cousins to each other.
Your mother's sister's children, sons or daughters, are your first cousins. The children of first cousins are second cousins to each other. That is the relationship between your children, or either sex, and your first cousin's children, of either sex..
If two people are first cousins, their children are second cousins. If two people are fifth cousins, their children are sixth cousins.