User blog comment:B214/Volume 22 spoilers/@comment-190.213.228.77-20160821180554/@comment-9595671-20160821191523

That's what I remember hearing too.

And I think we could hear more from EX too for the reason we know Issei and Le Fay has a son, but we only know him through mention alone.

That and it's said in EX Issei has atleast 20 kids, but I don't see that many girls in his harem if there's only one child per each girl. So perhaps we haven't met them because the other mothers still need to reveal themselves in the main story.