Food, if your there and have a way to warm them up a quick swim in warm water would be fine, i usually get mine swimming a bit at week old if they are me raised lol
I towel them well, and place them back under their lamp, warm the room up too, a rubber tub or a childs bathtub is a great option, even a kitty litter box, key again NOT long and warmth during and after, chilled babies is a top killer.
Food, is a massive motivator for ducks, i can get my 2 calls, 2 scovies and 2 buffs to eat out my hand(yes, all these fools are in my house right now!) it's so bad my buffs nibble at my hands the second i go into the brooder...
I take a plate, some chick grit and finely chop romaine, there are other things too have you seen the treat sticky?