>>108667002All the other kids being the same shape is a result of A) Homer becoming the main character B) Sloppy worldbuilding.
When the series started in the Tracy Ullman shorts Bart was unambiguously the main character, and he was also unambiguously fat. More gluttonous than his father even.
When the main cartoon started, the focus shifted to Homer, and the designs of Bart's classmates were pretty lazily done on Bart and Lisa's model. Which suddenly transformed Bart into a 'normal' sized kid instead of overweight.
Also, despite only meant to be merely overweight, as a 6 foot tall 235 pound make, Flanderization caused Homer to be treated as the fattest most gluttonous asshole in Springfield - even though it resembles nothing of his original characterization or design. Naturally, this meant if the writers were going to make a fat joke or a food joke they'd now use Homer instead of Bart. Minimizing this character trait in him.
