Those two ideas seems creative and inspirational enough to me!
In the vampire story I think you should go for a parent-child relationship like in the Logan movie. The father doesn't really care about the child at all, Logan didn't even know it was his child until she pulled out her claws. I really loved the scene where she went to a store at a gas station and just took stuff without paying, then Logan came in and yelled "Not okay!" To me that seemed like he was starting to parent his daughter in a way, and it really moved me.
In the dark lord story I wouldn't have anything against them being a male. The child too. But that's just my opinion, they could really be any gender. The thing that really counts is the story itself. I think you should go for kidnapping and make them have a weird/awkward relationship. The child should be raised in some private school with a high level of education (or the opposite, depending on the ending, read on), where he starts of not having any friends, but eventually making friends with three to five people.
Somewhere through the story the child should discover the the dark lord's plan and they should be against this. Perhaps friends are involved in some gruesome destiny. Now here's the thing. Either the child ends off killing the dark lord, or the two of them agree on something and makes it look like they died, kind of like (spoiler alert!) Lelouch from Code Geass.
The first story could turn into either a comedy, psychological or action, as what I can think of this instant.
The second story could definitely turn in to some mind game, and I love that kind of thing!
If you're interested in collaborating on these stories, be sure to hit me up! Leave a reply, private message, anything really. If you're interested in my writing style I'll leave a sample of a mind-twisting novel I'm working on. The language is supposed to sound a bit off, as the prologue is one of a series of mysterious incidents that first will be explained in the latter chapters when the actual story begins.
Sample of my writing: The Human Mind — Prologue: When Time Breaks Down