Indian Runner cannot walk

[Feathersnerd]

Hi, I have two very cute, very messy Indian runner ducklings. They hatched at the same time (48 hours ago) yet one is twice as big as the other one. The big one is penguin and the small one is bobble. They are both eating and drinking. Bobble cannot walk though and i was wondering how i can encourage it to walk. To get around bobble hobbles on its heel or knee

, has anyone else's ducklings done this before and how did you fix it if so. They are the cutest thing though. they think that i am momma duck. But they eat EVERYTHING.