These are obviously by Milt Kahl and predate animation on Jungle Book. It is pretty much the character you see in the film, but this early on Milt is still messing with Mowgli's overall proportions.
The size of the head to the body, the size of his hands etc. Details of his anatomy are already figured out. Legs, arms and the ever complicated way to draw accurate knees in any position.
Another feast for the eyes.
More on Mowgli here: