After the transformation was complete, their memories changed.
As far as Jon and Zoe were concerned, they were always 50 feet tall, since they didn't hear Mikey's wish. Jon reached over to Mikey to try and calm him down. For some reason that Jon couldn't figure, his brother was freaking out about being so tall.
As far as Jon and Mikey were concerned, they were both always one of the prettiest girls at their schools, since they didn't hear Zoe's wish.
And as far as Mikey and Zoe were concerned, they were both always she-males, since they didn't hear Jon's wish.
Jon now remembered that he made his wish because he felt too different from his siblings. They had very impressive dicks and Jon always wanted one. He knew that he would cease to be a girl if he did that, but he figured that it was worth it.