Bad choice for the mother's voice. And I get that was done on purpose. Its just more distracting then funny. On a side note I had to laugh when they tried to make joro seem like he was gay toward the end. Pretty funny.
Sun-chan and the mom sound about the same and act about the same. However, it's the sound of a 7-year-old girl. And in a high school student, it's her being a bit childish, in a mom, it's creepy and disturbing as they're most definitely in their late 20's or early 30's.