Now I'm imagining chubby Hiro growing a tiny bit (and putting on a bit more muscle although only Baymax can tell) and he doesn't notice how his clothes don't quite fit right anymore but he DOES notice that his wings are acting up a bit. He spends DAYS trying to work out the problem. It's hilarious and adorable. Eventually Aunt Cass notices and points out to Hiro that he's a whole half a centimetre taller.
She starts tearing up because her little boy is finally becoming a man. Hiro is incredibly embarrassed by the mushiness but is secretly pleased. Now that she mentions it, he does feel a bit bigger.
He starts measuring himself, height, weight, whatever, tracking his growth spurt with gleeful eyes, wondering if he’ll ever grow as tall as Tadashi once was.
(He ends up asking Sam how to get his wings to compensate for constantly altering weight, because he never knows when he’s going to grow. Sam rolls his eyes and starts complaining about “people who eat big breakfasts and like to throw themselves off of things without warning”, which confuses the heck out of Hiro, but then he helps Hiro out.)