When the kids barely reach the parents shoulders is the most annoying thing there can be. I mean, they're as tall as 10-year olds. When they're next to each other, then it's all fine - they all look adult enough. But when they're standing next to their parents, they look like they're adopted, with their biological parents much shorter than the adopted ones.
When you add to this some cases where the parents bodies have been enlarged, but their heads are the same size as their kids have, the annoying becomes grotesque.
Plus all the cases there where head to body or other proportions are off the scale, no matter if they're supposed to be kids or parents.
The cases where the character can barely fit through a doorway or legs are hanging over the edge of their tiny beds or they sit on enormous stools or chairs like kids, their feet hanging in the air, are just funny.
In other words, scaling and proportions are important.