User blog comment:B214/Volume 22 spoilers/@comment-201.215.165.7-20170213165134/@comment-29963364-20170214035032

"Reincarnated" means that you were originally something/someone else. If you were born as something/someone from the get-go, then you're NOT reincarnated.

So any child Issei has with other Reincarnated Devils will be  just a Plain Devil.