Okay I've got a webcomic idea, where Yahweh and Lucifer (who takes the form of a woman most of the time, mainly because she can make God look like a sexist jerk) out of boredom both made a child using mortal parents. God used an angel to concieve a child on a single woman who dearly wanted a child, resulting in Josephene "Josie" Magdalene. Lucifer possed a mother of four during a lovemaking session with her husband, resulting in Tariq (I need an Arabic last name that has something to do with morning star). Both children have incredible reality warping powers, and have always known of their origins. They meet in preschool and become fast friends. So what could be things that make the two stick togethor? Their story follows them from four to fiveteen. And does the idea have promise?
Maybe the devil's child is more exciting to be around, yet a troublemaker. The angel's child could be the good kid who's attracted to someone more adventurous. On the other hand, that's cliche...maybe find a plausible way to make it vice-versa? What if the girl raised by a single mom needs a father figure?
Tariq's actaully quite a warm bubbly child. Josie, when the story starts, is saintly, but so much so it's a bit creepy. Could that work. In fact I thought Tariq could help teach her to be more normal. So how could a saintly four year old be creepy?
Just make them people - I have a similar situation although their origins weren't as well known when they started school. Socrates is son of the true Father-Abbot and Nate the son of the Lord Evil. They go on to become lovers. I just made them normal characters people in their own right distinct from their parents. Nate chooses Socrates over his father. Their first day at school in under fantasy. Don't think of them as good or bad just give them good points and bad points.
It will depend on their personality and who else is in the class. With my two Soc is a Crown Prince and tends to hide so people don't bow towards him. Nate will punch someone that upsets Soc and fight with his brother. Nate is the popular class clown, Soc is more studious and quiet - he unfallingly loyal which earns him friends. He tends to be good friends with his teachers. Once you start writing and learn your characters they will tell you how they interact with others. Dont set their personality too much in stone before you start let it evolve.
Also the Grim Reaper's their teacher. And everyone in the town know about them. And could a perfect, saintly, wonderful little girl be creepy?
It has never stopped him communicating with people before - Think Joan of Arc. Well just think about it being the parent of Jesus must have been weird having a perfect child but not being a perfect parent - you are having a bad day and yell at him and he doesn't respond etc I always really felt for Mary and Joseph as I read that. There is a poem about it but can't remember the poet or the title. He goes missing age twelve makes you walk many extra miles probably a day off work and loss of finance and he reprimands you.
Would it be interesting to see Josie's mum relived when Tariq starts rubbing of on her and show's she imperfect and need's her mum and stuff?
So any way their friendship could help each over? Also how might the traits expected of a demonic child work out in such a way so that that Tariq's a rather nice kid to be around? And kiddy things they could use their powers for?
Opposing characters often attract each other. To the reader it may be obvious that they are the good and the bad, yet to your characters, young at age, they may not. When they are growing old you can weave in a separation theme. maybe something like a woman who is attracted to a serial killer. She knows he is bad, but he is so ... uh .... exciting. And of course he would never kill HER, would he ? (she won the innocence prize)
Tariq isn't evil, in fact he's a rather pleasent child. So is Josie, all though she can be a bit more unapproachable and weird.
I honestly think these are questions you won't answer until you start to write with them and learn more about them and how they function in the environment you are going to place them in.
A story concept means nothing. I can tell you now, it has all been done before. What matters is how you write it, the characterization, the flow, the imagery, all of it. There's no benefit in asking what other people think of the concept! They'll either say,"Sounds great," or, "it sounds like a ripoff of..." If the idea stirs you, write it. Then ask people what they think of the final story. After they tell you what they don't like about it, revise it, usually several times, until you're happy with it or until you throw up your hands and say the hell with it. Please read What is Plot Creation and Development? So your idea has as much promise as you can deliver with your writing. Personally, the idea doesn't appeal much to me - it has elements of a creation myth and elements of a superhero comic that sound like they would mix like whipped cream and asphalt. But go ahead and write it well enough to prove me wrong.