Continuity mistake: After his mother is shot, Erik squashes the bell on the doctor's desk. Its shape is completely different in all subsequent shots. (00:07:50)
Continuity mistake: When the young mutants are showing each other what they can do, they all have a glass of cola, all four sitting on a corner of the table. But when Banshee wants to show what he can do, the glasses are instantly lined up. (00:51:00)
Continuity mistake: Erik meets two Germans at the bar in Argentina, a pig farmer and a tailor. The amount of beer in the farmer's glass increases after Erik walks towards him. (00:23:20)
Continuity mistake: The Nazi doctor shoves a coin towards the edge of his desk, telling young Erik to move it or he'd shoot his mother. In a shot from behind the desk, the coin is much closer to the edge than in other shots. (00:07:15)
Continuity mistake: When Erik is first attempting to lift the submarine, he'd using his left hand. In subsequent scenes, specifically when Riptide turns into heavy wind to break Erik's grasp, he's now using his right hand.
Answer: It is shown in X-Men: Days of Future Past that Hank made a serum that can help him walk.