If the devil does have children, they are fixed in number.

And they are old. Satan had until Genesis 6 to have kids. That's a long time ago. And even if the number is legion, it is still fixed. No woman lives to bare the devil's seed. That woman ended with the flood, and just like lifespan itself, it would take more than nine months and breast milk to bring devil spawn forth. Logistics out the way, let us look at time. eyes
eyes
How old would those kids be? Moses showed up 1,400 years before Jesus, Christopher Columbus 1400+ years afterward. That's 2,800 years. 1492 to 2019, not to mention Moses to Abraham to Noah, who outlived the flood. 2019-1492=527 people. Moses to Abraham, at least 400 for slavery and time for Jacob, Isaac then Abraham. 500+ more or 1,000+. We're at 3,800 years to Abraham. eyes
eyes
Question mark from Abraham to Noah, but give or take six generations in reverse to Genesis 6. Our story began here. 4,000+ year old kids walking around! A 4,000 year old cannot walk around in public like normal people. Being half mortal, if they're dead Satan knows where each and everyone is buried. If alive, I'm not saying they're decrepid. Just careful.