LMBO
Okay, some people keep them in with chicks, but ducklings are messy with a capital M, and will outgrow them quickly. I have chicks and ducks the same age, about 3 weeks, and the ducklings are double if not triple their size. I prefer to keep them seperate. Chick starter is fine. There are issues with some of the medications that can be in medicated chick feed however, so you will want to check. Alot of people just prefer flat out to not give them medicated chick feed, so do some reasearch and see where you land. Flock Raiser can be used, and it is non-medicated as well as most organic starters. If you need a list of safe medications in medicated feeds, let me know, I have it in a book. Ducklings need more Niacin than chicks, and this is very important. Many people use Brewer's Yeast in their food, but others will add a Niacin tablet to the water. This should get you by for the first couple of weeks. Protien requirements change as they get older in the hopes that lowering the protien will stop the condition called Angle Wing. Some don't think it is a protien issue at all, but genetic, so again, more reasearch to see how you personally feel. Get Storey's Guide to Raising Ducks. It is jammed packed with info. Hope this helps!
Oh, and don't let them in water quite yet. I would give them a week, and then make sure the water is warm, and that they are at least towel dried and put under their heat lamp. Ducklings raised without a momma duck do not have the protective oils that keep ducklings "dry" even when wet, so they can get quite chilled.
Congratulations, you will love them!