magwai says:

Taking care of ducklings is honestly simple. There are a few dangers to be aware of but.
Keep ducklings in a warm and safe environment. A plastic tote works splendid for the first few weeks. Use a heat lamp with a 40 to 100 watt bulb. Adjust the height and wattage according to your ducklings behavior. If they seem warm and settled, not huddling under the lamp, they are doubtless warm enough. If they are scattered out, away from the lamp, panting, etc., they are too warm. Common sense will tell you to lower the heat. Hay can be used if available for bedding. By no means use newspaper or a smooth surface, as it could cause leg problems or a condition called “splay leg.”
Make sure heat lamps are secured and the area is large enough for the ducklings to get closer if they are cold and further away if too warm.
Ducklings that take a nap together in a clump are too cold or if they have their mouths open(panting like a dog)they are too hot.
Feed game bird starter, chick starter , or a commercially prepared waterfowl starter for the first 4-6 weeks. NEVER feed medicated chick starter or poultry feed, as this is fatal to your ducklings. Also anything moldy is FATAL to your ducks of all ages! Bread, although thought of as the ultimate “duck food,” is also perilous to ducklings, because it expands in their crop and chokes them.
Bread should by no means be fed to ducks of any age, especially those in parks and ponds. Use a plastic or galvanized feeder. Always provide clean, fresh drinking water. Use a shallow bowl to which you have added a few clean, small pebbles. This will preclude the ducklings from drowning.
You can also place clean pebbles in a store bought waterer if it is too deep Ducks need to be able to submerge their heads to clear their sinuses. DO NOT let them swim unattended. They MUST be able to get out of the water promptly. Ducklings can and will drown if they get too wet or too cold.
Ducklings will eat on their own immediately. You can add a small amount of sugar in their water for the first couple of days to help them get off to a excellent start.
Learn that Ducklings should be fully feathered before allowing them to swim. Depending on the type of duck, full feathers should be in place by 9-12 weeks of age.
Know that if you have other adult ducks in your pond/water source, be advised the older adult ducks can be fatal to your younger ducks. Older ducks may drown the younger ducks.

[edit] TipsAfter ducks are in the pond or water source, you may feed floating fish food or dog food in very small amounts. Switch their vital diet to a excellent quality unmedicated waterfowl or poultry allocation, usually available at most feed stores.
Generally, ducks will eat more during autumn and winter months, than in spring and summer months.
As ducklings will eventually grow into full sized ducks, a large dog kennel should make a splendid pen for your waterfowl, but a shed with a latchable door is best in terms of room and space.
Always place your ducklings in a safe cage at night, because they are very vulnarable to predators.

[edit] WarningsNEVER let your ducklings swim unattended, as they may drown!
NEVER feed your ducklings medicated poultry feed!
Bread is terrible for them, and anything moldy can be FATAL.
Always have clean water near food source, as ducks cannot swallow food properly without water.
Ducklings IMPRINT on people immediately. They look to you as their Mom. Be prepared to teach and train them, and to care for them properly.
Ducklings are very social animals, so by no means get just one. They need at least one companion, but preferably three or four.

[edit] Things You’ll NeedFeeder
Heavy and Shallow Water Dish
Hay or Bedding, clean towels, etc.(Do not use cedar or plain newspaper) Use caution as they may ingest particular substances.
Heat Lamp