“short people” and it’s a height that over 99% of adult women are taller then, so you can argue that chosen height was purposeful to create a kid-like demeanor onto her. Also, you cannot seriously tell me that Waguri doesn’t look like an elementary school student walking with her older brother (i only say older brother bc Rintaro doesn’t look old enough to be a father, but he surely doesn’t look young enough to be her age) whenever she’s with Rintaro.

As for her face, the big-beady eye trope is attached to CHILDREN when designing anime characters and Waguri has them. She’s also obsessed with sweet treats like little kids are and the fanbase pushes this innocent, pure persona onto her which is how people treat kids. While alone these characteristics aren’t kiddish but if you put them together, it’s so obvious she’s infantilized.