The children of your mother's first cousins are your second cousins. The children of your mother's second cousins are your third cousins. And so forth.
Your second cousins.
Your mother's sister's children are your 1st cousins.
Your children and your first cousin's children are second cousins. Your children and your second cousin's children are third cousins. And so forth.
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.
Cousin once removed.
Your uncle's grandchildren are your first cousins, once removed. They and your grand children are your second cousins, once removed
Your child and your great nephew's parents would be first cousins. Their children would then be second cousins. And if they have children, they will be third cousins.
Your cousin's sister is also your cousin. Your first cousin's children and you children are second cousins. Your second cousin's children and your children are third cousins. And so forth.
Your first cousin's children are your first cousins, once removed. They are your children's second cousins. Your second cousin's children are your second cousins, once removed. They are your children's third cousins. And so forth.
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 mum's cousins' children are your second cousins. This means you share a great-grandparent with them, making them part of your extended family. You and your second cousins typically have a similar generational level in the family tree.