Does a mother sheep feed its babies milk?

No. No birds feed milk to their young. This characteristic is unique to mammals alone. Only mammals have mammary glands, which are necessary to produce milk.

Ducks and geese do not produce milk, so, no they do not feed milk to their young. That is something that mammals do, of which waterfowl are not. Baby ducklings are hatched knowing how to find food and eat. The mother may lead them to a good spot for some tasty roots, but the ducklings know how to eat all by themselves.

As mentioned, no species of birds provide milk for their young. Some birds are fed on special secretions from the parent birds' crop, and these may even be called crop milk, but it is not milk in the true sense of the Word. Birds which feed their young with "crop milk" include pigeons, doves and flamingos.