It's pretty hard to tell if Chowder or any duck at the age of 6 weeks is a male or female... . When my ducks were about that age, they were a similar breed to yours, and they looked like yours too. I thought they were all females because they just got all their feathers and were basically pure brown. But after a while of waiting some of them had new feathers grown around their heads and necks and I could tell for sure.
If, in about a month or so, Chowder or one of your ducks starts getting green, black, or another color on it's head and neck it's a drake.
But you don't have to tell just by the appearance, as, if they are male, they will develop a drakes' characteristics.
The drakes have more of a raspy, quite voice... while ducks have a loud quack sound, and they quack way more often.
If one is a drake, then it will start mating with the other, too.
I hope this somehow helped! :3