The Hearts Society was formed (way back in this comic’s prototype and backstory, “The Odd Squad”) so that nobody would ever be able to say “the authorities are useless” with regards to magical mayhem. However, these particular demons are an extraordinary exception to this, and I’ll elaborate why in Chapter 18.  Of course, I should also note, that we only have the gangsters’ word that the demons even really exist… And of course, even after Valley Curse there’d be options for Jack to raise a kid…but sometimes you just have that selfish little urge to have a bit of your DNA out there. Even Jack knows that’s stupid.