I know its early for treats for little ones, but I took a couple mealworms and mashed them and sprinkled them on the food; it makes the ducks more interested in the food. If you could find live waxworms at a bait shop they would work too, just make sure you put in on top of the food so they...
I'd put you ducks in the brooder. I think it needs to dry out and I'm sure your incubator is pretty humid. I think it will still heal. :) Time will tell.