Having been a cat owner a while back now, I can imagine how frustrating it is to keep your moggy in.
I'm sorry to say, that ducks are a bit insular in their thought patterns. If they feel safe enough to have a brood, then they will return year in, year out. It may also be likely that the new ducklings will follow suit.
The best way to deal with them is as was previously stated, take them to the local river.
Next year, keep a sharp eye out for them and discourage their nesting ideas.
If they don't feel welcome, they won't stay around.