Is there any decent model of what actually happens when children develop theory of mind?

Along with having a suite of emotions and recognizing cues in others, it's pretty obviously a required piece of learning to read emotion for humans. Below a certain age, it's literally impossible to generate ideas like "the cat doesn't like that", since there's no space between "I like that" and "that is likable". But I don't think I've ever seen somebody describe what kind of structural or chemical changes are correlated with e.g. passing the mirror test.