Try looking on youtube, there are a lot of wildlife rehabbing types there that document how they take care of ducklings.
What I know: Feed them by putting very small pieces of salad in a bowl of water so they can feed off the surface.
@MyrddinEmerys I've heard, and at least one source agrees, that mother ducks may instinctually adopt any nearby ducklings.
@MyrddinEmerys when I helped out at a wildlife rehab we kept our ducklings on a small room lined with tarp. We had a small kiddy pool and we change the water often. We fed them regular duck feed and supplemented it with clovers that we found outside. We also make sure to keep our interactions to a minimum so the ducklings would not imprint on us.
Hope you can find a wildlife rehab to take it in soon.
@RandomStickman @MyrddinEmerys Found a set of orphaned wood ducklings once. So, of course we took them home.
Ducks do imprint but the critical period is very early, so likely not a prob.
Filled the bathtub for the critters, fed them earthworms and bugs and veg and sprouted grain (they're not going to find official duck food when they're on their own!)
Within a week they were hell on wheels, so we returned them to the city park pond they had to be from. They didn't even wave goodbye!
@MyrddinEmerys I raised this little chick on its own. I used a desk lamp at night to keep it warm and during the day a small PET bottle of very warm water with a bed sock over the bottle to be its "mother". I added a second bed sock to be the mother's wing and the chick knew exactly what to - dived under the wing.
He grew up to be an enormous healthy rooster, now living his best life on a farm with his own harem of hens.