The Case of the Stuttering Pig (1937) was a Porky Pig cartoon with "Supervision" by Frank Tashlin and "Story" by Melvin Millar. In it, Porky and siblings come to find out that their uncle, Solomon Swine, has died, and they have received a significant inheritence. The executor, Lawyer Goodwill, shows them the will:

I will and bequeath all my property to my niece and nephews. Love and kisses, Uncle Solly.

PS Bury me not on the Lone Prairie.

The lawyer also shows another note later on in the will:

PS However, in case anything happens to my heirs my entire fortune goes to my good friend, Lawyer Goodwill. Unkie Solly.

Goodwill, of course, plots to steal the money, and goes down to a lab to drihk "Jekyll and Hyde Juice", turning into a monster, and then speaks directly to the audience:

I'm going to get rid of those pigs, and you can't help them either!

calling the audience "big softies", and then calls out specifically "you in the third row", and says

And if that guy in the third row comes up, I'll fix him too. You big creampuff!

Goodwill's plot unfolds, as he kidnaps Porky's siblings one by one, until only Porky is left. Porky, in running away, manages to find the lab where the prisoners are, but the monster corners all of them at once, and then -- a chair flies and hits the monster.

The pigs: Who did that?

Sound from the audience: Me!

Monster: Who are you?

Sound from the audience: I'm the guy in the third row, ya big sourpuss!

...

How much of the above did the audience "understand"? It certainly wasn't exclusively children, but not exclusively adults either:

A 1925 study of Middletown, Ohio found "about two and three-fourths times the city's entire population" went through the theater "during a typical month". (The study was repeated in 1935 without much difference.) It was a raucous mixture; some theaters were more "working class" and some were more "white collar". But typically, you had a lower-to-middle class mixture, and both adults and children (unaccompanied children, even).

The program wasn't typically just "one cartoon and a feature" but a mixture: maybe a short documentary or newsreel and a singalong, and one or two features. For the most part, "proper" etiquette was encouraged during these parts of the program, but for the Warner Brothers cartoons in particular you had an entirely different atmosphere: one that was more like an old vaudeville show, with chatter, disruption, and groups breaking out in song being the norm.

The cartoons leaned into that; they thrived on it; they routinely broke the fourth wall. They certainly had satire -- and playing with the idea of a vaudeville-style audience literally being inserted into an animated story reflects that -- but it was a mixture of the high and low, sometimes simultaneously.

Not every reference was catchable by everyone, of course (the title is meant to parody a Perry Mason film, The Case of the Stuttering Bishop) but, in essence, catching any of the layers was the "correct" way to watch.

(Although reactions could be odd. Chuck Jones tells a story about an animator who joined after WWII and wrote to his grandmother in Denver about writing scripts for Bugs Bunny. Her reaction: "I can't understand why you're writing scripts for Bugs Bunny, he's funny enough just as he is.")

Those working with WB did specifically have adults in mind; Chuck Jones states the cartoons "were absolutely made for adults".

This can be most strongly be seen by what got censored. Some animators took to "redlining", a practice that still happens today which is known as "cutting to a hard R". Basically -- put in more than the censor board will accept, in an effort to keep some of the "milder" offenses that would normally get cut.

For example, The Wise Quacking Duck (1943, directed by Bob Clampett) included a scene of Daffy doing a strip tease; it was intended to be one cut by the censors, but somehow that one got through. The same director's Scalp Trouble (1939) includes a moment where Porky's mouth moves but nothing is said; Paul Mullar (who worked in cartoon censorship) claims the actual lip-synch that got removed are the words "son of a bitch".

Or consider Tex Avery, who was with Warner for a time although he hopped studios to MGM (he quit putting in effort so he would be fired from Warner, and ended up becoming head of the MGM unit in 1941).

MGM (and Tex Avery) made the famous Red Hot Riding Hood short. If you haven't seen it but have seen Who Framed Roger Rabbit, the scene in the nightclub with the eyes popping out is a reference to that. The Big Bad Wolf falls over himself upon the performance of an adult Riding Hood in a nightclub; Red rejects the Wolf's advances, and the Wolf himself is perused by Grandma ("At last, a wolf!") After a chase where the Wolf escapes with severe injury, he ends up back in the nightclub and swears off women, saying he'll "kill himself before he looks at another babe." Riding Hood then goes back on the stage, so the Wolf commits suicide with two pistols, although his ghost rises up to continue hooting for Red's performance.

It was MGM's most profitable short. They had a screening in New Jersey where the audience went wild; the projectionist had to rewind and show it all over again, then show it again a third time at the end of the show.

Even that short had a sort of "redlining" -- one censor felt like the short promoted bestiality, so wanted a scene where the wolf removes a mask to show he is a man. This was made to appease the censor but was edited back out in the final version.

In short: the creatives who made the big output in the 1930s and 1940s didn't really write "for children"; at their most general they wrote for all audiences, at their most specific you have someone like Tex Avery who (in his own words) "leaned more toward the adult audience." Whether a particular satirical point was understood isn't recorded, but for some jokes -- like involving the audience in the story itself -- it can be equally fulfilling just as a gag, or as a reflection on class-distinction between behavior norms in "low" and "high" theatre.