Plural verbs

My daughter -- 2.5 -- is a veritable fount of linguistic curiosities. Of late, she has evidently become aware that something is different about a sentence in which the subject is third-person singular. In normal English, the verb adds an "s" most of the time: "I want to go," but "He wants to go."

But for my daughter, the extra "s" attaches to the subject rather than the verb. "Hes want to go," or "Its make me happy," to quote two of many examples that I've recently heard from her. She has never heard anyone else do this, so it can't be that she's repeating something she heard. And I'm sure she'll quickly grow out of it, as her brother did. But it's still fascinating to see how grammatical rules begin to formulate in her mind. (Actually, what's interesting is when rules malformulate, to coin a word from "malformed.")