Common Sense Note
Parents need to know that this classic top-cop vs. the mob drama has bloody violence and deaths of heroic and sympathetic characters, principally in shootings (including head shots) and shotgun blasts. A bomb explosions kills a child, and another in a baby carriage is nearly caught in a crossfire. There's a messy aftermath of a notorious shock scene in which Al Capone beats a character to death, just offscreen, with a baseball bat. Swearing is heavy ("f--k" and "s--t," etc.). Most characters smoke and drink.
Much shooting with revolver, rifle, and shotgun, with and bloody wounds and death (including head shots). Capone fatally beats a man with a baseball bat. Bomb blasts (one of which instantly kills a little girl). A villain falls to his death from a great height.
Plenty of swearing, including "f--k," "Goddamit," "whore," "s--t," "ass," "piss," and "Christ" used as an exclamation. Also, some ethnic slurs, like "wop."
Somewhat mixed message: It is possible to resist overwhelming public corruption. But to bring down a crime lord, "incorruptible" Eliot Ness must cross the line himself, becoming a liar and a revenge-driven murderer. In short, good guy must be more ruthless than the bad guys.
Drugs / Tobacco /
The Prohibition era and drinking alcohol are key elements in the plot; Ness orders police not to drink while Prohibition is in force (smoking is OK, though), though even the heroic "Untouchables" drink when nobody is looking. When Prohibition is lifted at the end, Ness himself turns out to be a drinker.