Q:

Is "except for not today we didn’t" correct?

Me and that Grace sit together on the school bus. Except for not today we didn't. Because today Grampa Miller drove me.
(Junie B.Jones)

In 2010, when I asked the meaning of the highlighted sentence in a Korean forum, a man replied it’s a wrong sentence. And I got a new one yesterday that says it’s a double negative, and meaning “Except for today we did.” Which one is right? If the second one is right, would you parse the original sentence for better understanding?

A:

Junie B. conflates three different Standard English expressions into one completely non-idiomatic one.

Except for today, when we didn't.  
Except today we didn't 
But not today: we didn't.

Junie B. uses "except for" where Standard English would use "except" elsewhere in the book. And in colloquial English you might very well hear any of the first pieces combined with any of the last pieces, for emphasis or just as a venial mistake. But the author is multiplying the errors as far as she plausibly can, to represent the speech of a 6-year-old who is inordinately, and quite mistakenly, proud of her command of the language. 

