Chibiverse
Some animated series, especially from Japan, switch one or more characters to a Super-Deformed art style for a moment as a take of sorts and then switch back to a taller "standard" proportion. Other series, especially E/I shows for preschoolers, consistently draw all characters three and a half heads tall or shorter. We can call this all-Super-Deformed-all-the-time art style a "chibiverse", and the choice to use this art style ends up having effects on how other tropes work.
For example, the size relationship between head and hands affects how much of the face a Face Palm covers, as seen in Garfield from 1996-12-30
. Head size also affects how much material is needed to make a hat compared to the rest of one's clothing, which in turn affects to what extent a hat can be used for carrying things (for example, Abraham Lincoln often carried papers in his top hat) or as a weapon. One might make a hat out of an old shirt in real life or vice versa in a chibiverse. Or the old wives' tale about losing most of your body heat through your head might be true, which could justify Never Bareheaded and give a good cover to identify characters with Only Six Faces by a hat.
Not all use of consistent SD proportion in a work is a chibiverse, however. Several series use a super-deformed art style to represent a universe whose inhabitants canonically have realistic proportions, much as third- and fourth-generation video games did. For example, the Super Deformed Shorts are an Art Shift of Avatar: The Last Airbender. You can tell a universe is a chibiverse when its characters are drawn SD even when they cross over to works with realistically proportioned characters, such as Earthbound 1994 and Animal Crossing characters next to Samus, Link, and Captain Falcon in the Super Smash Bros. series. When the art style originally used for a character persists across works using different art styles, it's probably seen in-universe as more than a mere art style, much as art style differences in Kappa Mikey are treated like race.
Children in a chibiverse would have to be tiny.
In Real Life, human heads already push the limit of the birth process. They're already as big as they can be without breaking mommy's ability to run. Even after the obstetrician cuts an opening to make the hole bigger for the baby's head, the head still has to squeeze to make it through. Before modern times, Death by Childbirth was common.
And yet cartoon characters' heads are even bigger, especially in TV shows for preschoolers. The super-deformed proportions seen in cartoons like Bob the Builder, Dora the Explorer, and Handy Manny are just anatomically impossible unless newborn babies in cartoon world are the size of newborn kangaroos.
"The stork brings babies. Therefore, solved." In a universe with Funny Animals, a stork obstetrician would run into the same problem. Even in universes that interpret storks as adoption agents, where children are produced somehow without the mother's pregnancy, newborns have to be small enough for something smaller than a Giant Flyer to carry. This means that in a chibiverse, the head would have to grow even more than it does in real life. And this is why cartoon parents have Pint-Sized Kids.
On the other hand, they could use the kiwi method: an egg half as long as the creature, which squeezes the stomach so much that the mother can't even eat toward the end of the pregnancy. But that might be too much Body Horror for a work targeted at single-digit-year-olds, and any deconstruction of chibi gestation would need to tread very carefully in order not to alienate the audience.
