Super-Deformed/WMG

Newborn babies in SD universes are positively tiny.
In Real Life, human heads already push the limit of the birth process. Even after the obstetrician (who is probably a stork in universes with Funny Animals) 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. And no, it isn't always an art style the way Chibi Avatar is to Avatar: The Last Airbender; characters in some universes are drawn SD even when they cross over to works with more realistically proportioned characters, such as Earthbound characters in ''Super Smash Bros. Brawl''.

This is true 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.

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.
 * human heads grow a bit in real life, human heads grow a lot in a chibiverse. Though they would be smaller than regular babies, but only because all humans are smaller in a chibiverse.
 * ...and I just realized I explained the biology of an artstyle.