(Many items have been moved to the Spoilers section. To provide the information parents need to decide which kids should watch the movie, consider summarizing the amount and type of violence shown, rather than lengthy descriptions that reveal a lot of plot.)
A man is hit by a car. Very little blood is seen, and the scene lasts for 3 seconds.
Two men fight bare handed and both suffer extremely bloodied faces before one man knocks the other man to the ground after driving his face through a car window and driving a fist into his face a dozen times (we see the battered man with a bloodied, swollen, poorly stitched face as he receives a mug shot and we hear that he went to Alcatraz).
Hooded men break into a man's home and use guns with silencers to shoot and kill the man, his wife and his maid, who all fall motionless to the floor.
In a public lunchroom, two men approach another man and a woman at a table; the man stands up, knocks both of the other men out, takes a bottle of acid from one of them and pours it onto the man's clothed crotch, which we see burn with smoke as the victim screams, "You'll get yours!"
Three men are locked into an elevator by their boss and we see a wall of flame shoot up the elevator shaft and hear screams as the camera cuts to a street scene.
A woman is slapped. A man comes in and shoots the person who slaps her.
A plainclothes police officer questions an informant on the street, twisting the man's arm and hand until blood appears on one finger.
Two detectives argue briefly and one punches the other in the eye, cutting it, with a little blood showing.
Undercover police break into the back room of a nightclub where a telephone gambling operation was underway, shooting up the phones and knocking guards and other men unconscious.