Noooooo! It's all to with commonality of grandparents. Your parents' siblings' children are your first cousins because you share a common ancestor - your grandparents.
Your cousin's children are your first cousins once removed, because you are of two different generations, ie you are the grandchild of the common ancestor, they are the great-grandchildren - one generation removed.
If you have children, then they and your cousins' children will be second cousins, because their common ancestor is a great-grandparent - two generations removed.
As jno says, complicated marriage scenarios don't change the fact that your dad's sister's (and your mum's brother's) kids are your cousins.
There's a chart about a third of the way down the page on this link that explains it all:
http://en.wikipedia.org/wiki/Cousin