There's absolutely nothing about Levi's size or his condition that bothers Erwin, other than perhaps he thinks that Levi deserves something better. Those aren't things he can do anything about right now, unfortunately. But food is, so he's happy to do even this much.

Levi's hand feels good in his - the difference in size isn't that great (not as much as it will be eventually), and they fit together easily. Erwin feels reluctant to let go at all, holding on until he ends up carrying things with both hands.

But for now he thinks a moment. "I don't know if one is better, I think it just depends on what you like - but we can get one of each and share so we both get both. Is that ok?"

Or maybe if they take too long to decide the merchant might just give both to both of them.