duckling sexing

[Cha Cha Chicken]

I have a pair of 3 week old ducklings (this is the first pair I've ever had) and was wondering how old they have to be to be sexed.
If they can be sexed now, I'll post some pics for help.
thanks!
oh, and if it makes a difference, I have a khaki campbell and a rouen.

 

[AnaD]

I have 3-4 week olds and one has started to quack already

. Only females quack.
https://www.backyardchickens.com/forum/viewtopic.php?id=181147

 

[MissusDee]

They will probably quack or "whisper" soon (within a week or two), so I would wait, rather than trying to say vent sex them. Sometimes you can tell by the bill, but it may be too early for that right now.