I'm writing a comedy, and the first chapter includes a 4-year old. How do I make their dialogue and behavior seem natural? I've read that I should misspell and leave out words, but I need some more specific advice. How do they act? How do I make them not seem cliche?

I can maybe help? I have an honours degree in psychology and had child psych all the way from first year to honours. It was a while ago though, and a lot of the theories are constantly being developed (since there are so many variables both internally and externally that contribute to the development of the child), but I can give you a rundown or answer some questions?

Yes please! Do you need background on the character?

I'd say don't overdo it with making their dialogue "childlike." A four year old will know some basic grammar and can form whole, but simple, sentences. And you don't need to misspell unless you're talking about using something like "goed" instead of "went." Kids that age are very smart and creative. They love to play pretend and can come up with pretty elaborate stories that may not make much sense to adults. If they're quiet, they're not dumb, they're standing there figuring stuff out and you can see the gears turning behind their eyes. They're not amazingly smart either and they don't spout off wise sayings, but they'll ask how things work and why you're doing something. Just give a child a unique personality and motivation like you would any other character.

^ yes

And they ask 400 questions a day, according to science.

Thanks for the advice :) I actually can't use most of it because the character is so short-lived (dies in the first chapter), but I'll keep that in mind

In my opinion the key to making them sound authentic is to have them use creative ways to get around lack of vocabulary. Some examples from my 4yo kids “My eyes are seasick” because wind was making her eyes water. “Long chicken” was a request for chicken tenders instead of nuggets. “Lotions to William” when my son felt his skin was too dry.

My kid is turning 4 in September.
Lots of mood swings, wanting to be a big kid - but not when it comes to having to help or tidy or sometimes walk a distance.
Difficulty when she has some kind of plan in her head - an reality dares to differ. Even small things, like she expected to get strawberry jam for breakfast and there was none left. Big drama!
Often contradicting herself - which kind of goes with the moodswings. Make her choose one candy, she eats it. And starts crying, because "but I wanted the other one".
Of course there is the good stuff, like telling us a lot about what she did and heard through the day. Often telling us about stories from a book or from a kid's CD.
Starting to take care of others, like having guests and making sure they all have a drink.
I hope that makes sense and helps...

I'm interested to see a comedy where a child dies in the first chapter, lol.

@scatmandingo @igot3bodyproblemsa That's actually really helpful, thanks so much! @unicycle The chapters are written around jokes, so the kid sets it up, and then dies as a result of it. It sounds weird, I know

I came to say "please don't make them make a hundred mistakes to be cute" (because I already hated that back then) then moved on to "oh yeah so many questions at that age" (sometimes they also make weird associations in their heads, like I asked a group "why did monks copy books?" and that girl said "wikipedia". We were all kinda puzzled but by furthering questioning her it appeared she meant "they wanted to make a knowledge bank, like an old timey Wikipedia") and now I just really want to read your story.

Idk if this helps, but maybe take a look at "kids say the darndest things" ? Might give you some ideas on child speech patterns/thought processes that people have found comedic. Admittedly they tend to be a little older than the age group you're thinking of.

I'll check it out, thanks :D

All of this advice is great, I think the best method to getting realistic dialogue is to just talk to a 4 year old. Do you have any cousins or maybe nieces or nephews? Even a friend with a kid around the same age.
If not then go to the internet. There's plenty of videos of kids talking. When I did phonetics and linguistics/ child development I learnt the most through the endless case studies we had to do of kids talking, you learn about their general mannerisms and utterances. If you have access to this book called the Introduction to Speech Language and Literacy by McLeod, that would help you a lot. Or you could google "Pragmatics of 4 year olds" into google scholar and you'll find the rules and structures of their speech patterns. Depends how in depth you want to go with this character.

I don't have any family members that age :( I'll make sure to take a look at those videos though! Thanks so much :)