Bugs, bugs, and more bugs. And a side order of worms. If you are hand raising them - some Gerber rice would be a good thing too - between the bugs. If you do not have a yard full of bugs for them to forage on you can buy meal worms in the local pet store - the local feed store (that usually sell chicks and ducklings in the spring) would be a great place to call and see what they have and recommend for feeding. I would trust the info from the folks at the feed store over most other people.

Go to your local feed store and buy proper duck feed for these baby ducks It has to be for babies since their systems are not ready for adult foods

Here is a site that tells all take a look

http://www.liveducks.com/care.html

I saw an article the other day about this, let me check my history real fast and I will get back with the link