The vs. Duh

Apparently while learning the alphabet sounds at school someone said that the letter 'd' says 'duh' which I assume some kid has an older sibling who says, "Duh!" which is not a word that Julius or I have ever used. And although the 'd' does say 'duh', Alexa has learned to exaggerate the sound into "Duh!"... which she then started confusing with the word "the"... This is driving me bonkers, because it is such a minimal sound change between the two that I don't think Alexa realizes the difference. She always says, "The letter 'd' says duh mom, that is just like the." Which it is not just like 'the'... Hopefully this will not cause future problems, and she still wonders why some kids say, "The!" As in this conversation she told me about:
Child 1: "Your sitting behind Aaron."
Child 2: "I already know that, the!"