Great Now according to this article below I have three drakes and one duck!

Barrowed from this website
http://community-2.webtv.net/saraarmstrong/EggDucklingHelp/
Sight Sexing Ducklings! (for Khaki Campbell's only)
There are 2 kinds of Khaki Campbells. Light and Dark.
The Darker Khaki's are a darker shade of khaki brown. The Light Khaki's are a lighter shade of khaki brown.
Now comes the interesting part, you have to look at the bean on the end of the bill. The adult males have a darker bean then the rest of their bill. The adult females have a bean that is very close to the color of the bill.
You won't be able notice the difference until 4 to 6 weeks of age. As they grow you will see a gradual change as the color deepens. Then one day it will be just as plain as the bean on there bill

Here are the adult bill and bean colors:
-Dark Khaki Campbell Drakes has a bluish green bill and black bean.
-Light Khaki Campbell Drakes has a yellow bill and a medium brown bean.
-Dark Khaki Campbell Hens has a slate gray bill and bean.
-Light Khaki Campbell Hens has a slate gray bill and carmel colored bean.
-I have one Lighter Khaki Campbell Hen who dosen't quit fit the standard, she has a medim brown bill and a carmel colored bean. She's very cute and sweet.
Another difference between a male and a female duckling is at 5 to 8 weeks of age. When the male's head and the neck become a shade or two darker then the body feathers. The female feathers are a uniform shade of brown.
A male is about 20% larger then a female.
Now if you think you have a good ear, the voice of a young male is different from a female. As adults the male has a raspy voice, in younger males you can sense that raspy sounding voice. But, it is a challange to detect it. In females the voice is a clear quack and in the young females it sounds like a squeeky toy.
Now, this won't work for most other breeds of ducks, because the bean may not be darker in the adults