I'm afraid I'm not a duck person but your little ducks sure are cute You would be best posting your pics in the duck section of the forum. Here is the link ~ https://www.backyardchickens.com/f/42/ducks
I'm more than sure the duck experts over there will be able to help you.
I have calls and those look a bit young yet to tell... about when they start feathering in really well, their voices will change... the boys will have a lower, quieter, raspy wha-wha sound and the girls will have a higher pitched, much louder and quicker quack-quack-quack sound...