This seems super cool! I have a few ideas that I've been too busy with my writing comms to do, so maybe jotting a few down here could help you out, lol
Gender/appearing gender: Mostly feminine, maybe bordering on femboy? (They'd be Enby, so an androgenous look is ideal)
Species: Angel/Hellborn Hybrid (Hazbin Hotel, if you couldn't tell, lol. Dad would likely be the Angel, and extra bonus points if it's clearly Adam's kiddo!)
Moodboard or aesthetic: A glitchcore/cyberpunk type of aesthetic? Or maybe a cyber punk horror theme, mixed with a bit of Cosmic Horror/ biblically accurate angel aesthetics? Lots of  floating eyes, wings/tentacles. Go crazy!
Clothes/outfit: (optional) N/a, Go crazy with whatever ideas you have!
Other notes: Mentioned this is a Hazbin character, and the idea was based on a weird af dream where Adam had a kid with An imp for some reason. The demon/hellborn half doesn't have to be an imp, but it's definitely preferred. Other demon types for the mom's half could be a goetia, or even based on one of the Deadly Sins in Helluva Boss, Like mammon or Ozzie. As long as there are design Elements to show it's Adam's kid, go wild with it. If you want to design the mom too, feel free! Especially if it would help.