Sexing Ducklings

[HeatherFeatherFlock]

We have 8 khaki Campbell ducklings, we hatched them ourselves. We want to keep 2 girls and sell the rest, hopefully all to one person.
We tried vent sexing but they seemed to “all be girls” so I don’t think I did it very well, lol.
What other ways have you found you can tell which can help you tell male or female?
I’ve heard of different quack sounds but maybe only as adults?
I’ve heard of slightly different head shape as ducklings???
They are 4-7 days old.

 

[DiYMama540]

Very difficult to sex the ducklings until they get a little bit older. The voice sexing is the most accurate. I'm thinking my ducks voices started to change around 4 weeks.

 

[chickens really]

I can usually tell because Drake Ducklings have melon heads and the hens have a more delicate head and look to them.