I hatched ducklings last year (6).
I left out a ~8 in long 2 in wide tray (corn cob plate lol) of started feed (NON MEDICATED) and I dribbled water in it to make it mushy when they were under a week old. They ate that up within 6-12 hours and I filled it up when ever they finished (so food availible 24/7).
Keep water available in this: (
http://www.tractorsupply.com/tsc/product/little-giant-1-qt-screw-on-poultry-jar http://www.tractorsupply.com/tsc/product/harris-farms-screw-on-fount-base-1-qt) DO NOT KEEP AN OPEN TRAY/BOWL OF WATER IN THE BROODER. The ducklings will try to swim in it, will make a mess, and will soak the bedding.
Beware, when keeping ducklings, you will have to change the brooder almost bedding everyday or else it will stink like sour cream gone bad.