TV-G for television airings, whereas NR (Not Rated) when they aired originally.
Violence is pretty minimal, in many shorts, the characters use guns, TNT, slapstick etc.
Language is very mild, considering the TV rating is G. In the 1961 film "The Rebel Without Claws", the word "damn" is used twice. Also, in the 1941 short "The Fighting 69½th", a swear was supposedly mouthed.
Sexual Themes and Nudity:
There are hardly any, but in two cartoons, characters are seen reading parodies of Esquire, which was considered quite racy back upon the cartoons' release. The spin off Animaniacs references sexual jokes and innuendos in the show.
This series was built on crude mischief. Characters experience so much of this that it even went so far as to have Porky Pig be hit with a WB shield in the 1938 short "Porky in Wackyland". In the earlier cartoons, racial stereotypes were used, as it was normal during the time, though this usage is less frequent in later cartoons.