Put using a mortal would be the best way for you to get a mini-Tizzy to mold in your own twisted image. A demoness would have control of any pure child, but you could easily over power a mortal mother for your demonic offspring’s nurturing. You could also lie through your teeth and make it seem like their mother wanted to kill/abandon them, which could be true, always good to have an heir. They can be consumed with vengeance upon your death. It’s what all parents want. A child consumed with hatred against their parents killer, whom they will pursue with the entirety of their being.