I call fake on this one. You SERIOUSLY think they'd have a child in the middle of a war? And Snape was still a Death Eater at this point, and the Potters were hiding, why would Lily risk to go out and make peace with someone in an orginization that was destroying the world and wanted her family dead?And the godfather still would have been Sirius again or Remus (or, Peter ugh) BUT THERE WAS NO OTHER CHILD. This is the most absolute dumbest 'theory' (if you can even call it that) I've ever heard. Rant over.
*starts crying in corner*