I agree. I don't think there's gonna be a non-alchoholic Duff. This isn't the same as Butterbeer; it's for a different demographic. There will probably be other themed drinks available for the under age guests, like Squishees!
BTW, you can see the beeramid to the left of Moe's door!
And notice the entrance arch thingy for "Krustyland: The Krustest Place on Earth"