Oh dear, Khaki s are my favorites too.
I do wonder as they are the best egg layers,if they have been penned up in the hope that they could be used for that purpose and are afraid of the freedom now. Do you know their sex? How young are they?
I would feed them up as quick as you can . They are very gentle friendly ducks, although tend to be shy, so probably will come round if given some good grub and some attention.
Good luck, ah I feel sad now but glad you have them
XX Jeannine