Do the legs seem spread apart like splayed legs? What is the ducklings being fed? Ducklings do need Niacin in their diet, you can purchase capsules of them at Walmart. Where is the duckling being kept? What's the temperature the duckling is being kept in? What kind of bedding are you using for the duckling? What were the issues when hatching? You should't help a duckling hatch unless it's been at least 24 hours since pipping and the duckling hasn't zipped yet. This can really hurt the duckling, especially if they weren't ready yet and haven't absorbed all of their yolk. Ducklings know when it's time for them to hatch. Where and how did you help the duckling hatch? Did you let the duckling dry and fluff up in the incubator after hatching? I suggest getting some poultry electrolytes and vitamins to give an extra boost. There is a possibility that the duckling is disabled or has something neurologically wrong. Ducklings are weak and get tired, but they're usually walking withing a day or two after hatching. This is not normal... Do the eyes look normal [ dark, glossy, clear ] ?
I wish the best of luck for you guys!

I hope I can help!