Effectively the same thing as a
cinnamon roll. (A character or person who is adorable/innocent/precious/cute and must be
protected at all costs, but may or may not be exposed to
constant pain that they do not deserve).
The only difference in usage is that cinnamon roll is less common and does not generally imply that the character/person is in constant danger.
Person 1: "How did his ex do that to him???"
Person 2: "
IKR,
how could you hurt a
cinnamon bun like that?"
Or
Person 1: "have you seen the new kid?"
Person 2: "yeah, he's such a cinnamon bun."