When Gen and Shinji take a big bite from a sweet potato from each end, they are then told by Eiko to give the sweet potato to their mother. Once the sweet potato is given to her, it is whole again.
When the boys are about to abandon Seiji, his hands are bare and his feet only partly bandaged. By the end of the scene, seconds later, his extremities are fully covered.
Neither of the atomic bombs dropped on Japan in the Second World War used a parachute. Both dropped in free fall.