My flock of six week old goslings was caught in a rain storm and they are lying all over the yard and are not moving. Both goslings and ducklings are very vulnerable to hard rains until they are well feathered. If found quickly, they may not be dead. Try reviving them by placing them under a strong heat lamp or even in an oven set on a low temperature and door open. In either case, towel them as dry as you can and then keep your fingers crossed.
Speed is of the essence.
I do not let young ducklings or goslings outside for extended periods unsupervised until they are well feathered over the backs. Do not assume that because some sort of shelter is provided, that they will have sense enough to use it. Q. My flock of ducks sleeps overnite in an area in front of our barn which is protected by a big yard light. There was never a problem with predators until recently when I began losing one or two birds a night. Sometimes there was nothing left and sometimes only the head of the victim was to be found.