For the bees, they pulled the straw out of the Scarecrow, covered Dorothy and the Lion, while the Tin Woodsman stood out in the open. As the bees attack, they just broke off their stingers on his metal skin, building up piles of dead bees until they looked like piles of coal. When the crows attacked, the Scarecrow stood out in the open and as the crows flew in to peck his painted-on eyes, he pulled them out of the air, wringing their necks. Again, huge amounts of dead crows stacked up. When the wolves attacked, the Tin Woodsman lopped their heads off with his ax.
No action from the Cowardly Lion, but later on he breaks the back of some guardian monster.
Pretty gruesome stuff and I'm sure the masses expecting a musical or kids movie would be outraged.

The story of Nick Chopper, the Tin Woodsman himself, is pretty violent, as his cursed ax systematically cuts off parts of his own body. The depiction of his body parts being replaced, piece by piece, with tin parts could be played out rather darkly.
After Dororthy and the Lion fall victim to the poppy fields, the Woodsman sees a mouse being pursued by a wildcat. Feeling for the mouse, he cuts off the head of the wildcat (I guess his compassion only goes so far), rescuing the Queen of Mice, who helps them get Dorothy and the Lion out of the fields.
The attack of the Winged Monkeys result in the Scarecrow being ripped apart, his straw scattered and the clothes that make up his body thrown into a tree (although this was done in the 1939 version, to an extent) and the Tin Woodsman is flown into the air and dashed down onto huge sharp and jagged rocks, mangling his body.
On the way to see Glinda, the quartet encounter a land where the people and animals are made of china and subsequently, very fragile.
The Cowardly Lion gains his title of King of the Forest by defeating a huge insect monster that terrorizes all the other animals. He jumps onto the monster's weak point in its back, breaking it, then swiping its spiderish head off with his mighty clawed paw. Baum was big on decapitation, sounds like.
The also meet men called the Hammerheads at the top of a hill, who threaten to stop their progress. Since the Hammerheads have no arms, Dorothy and company are puzzled how the Hammerheads will stop them. When they get close, the Hammerheads' heads spring out on their extendable necks, knocking them back down the hill. Not really as violent as some of the other parts, but bizarre enough.