Your first cousin's grandchildren are your first cousins, twice removed.
Your second cousin's grandchildren are your second cousins, twice removed.
And so forth.
they would be second cousins
They would be cousins to some degree. They are 2nd cousins.
Your grandchildren and your grandniece are second cousins to each other..
The grandchildren of your grandmother and the grandchildren of any of her siblings (including of her brother) are second cousins to each other.
Your grandchildren and your niece are first cousins, once removed, to each other.
The name of the relationship between your grandchildren and your sibling's grandchildren is called being "second cousins." The genetic relationship between two families becomes smaller and smaller through each generation, but no matter how weak that relationship is, it's still counted as a blood relationship. Your grandchildren and your sibling's grandchildren share a pair of great grandparents.
They are first cousins once removed. Your niece's children and your grandchildren will then be 2nd cousins.
They would be second cousins. Your child and your grandniece's parent are first cousins. There are no 'removed' involved because the generation difference between the common ancestors (your parents) is the same.
Your great uncle's kids are your parent's first cousins. His grandchildren are your second cousins.
Your father and your aunt are siblings (brother and sister) The grandchildren of siblings are second cousins to each other.
If you are referring to YOUR grandmother and grandfather then your children are their great grandchildren. If you are referring to your parents, then your children are their grandchildren. The primary kinship dominates.
The common ancestor is your parents. Your children and your sister's children are first cousins. Your grandchildren and your sister's grandchildren are second cousins. Your great-grandchildren and your sister's great-grandchildren are third cousins.