chick4chicks is right. Iif you can get game starter in small bags for just 2 ducklings. Up until a month ago I couldn't get game starter even in the 50# bag. Now I can and will use it for the quail and ducklings when I have more. But my last ducklings were on chick grower and you'll be using that soon for your chicks anyway.
What ever you use, just make sure it's not medicated.
Start giving the ducklings, greens right away, chopped fine, or mashed peas, green beans. Provide grit free choise (sand or chick grit), once you decide to give them or your chicks treats. But with ducks, greens are necessary, not just a treat.