It is very hard to make the "generic" character interesting, especially if another character next to him is more enjoyable to read about. So my best advice is that you shouldn't worry too much about it. Just write down what feels right to you right now. Because it seems like the kid character never was meant to be that memorable anyway.
When I read about your story idea, I immediately thought about Karlsson on the Roof. It is about how an ordinary boy meets this utterly mischievous fantasy being. Of course, even if Lillebror is the protagonist, he is mostly interesting only as a contrast to his more colorful friend Karlsson. But that is only natural and not much to worry about.
Edited by Kickisan on May 17th 2020 at 1:13:51 PM
But if you still want to make the child protagonist at least feel a bit like a person rather than a passive faceless narrator, consider this: how did the child wind up hanging around a magical being in the first place?
Did they find a magic portal while playing in the woods near their neighborhood? Was the kid playing in the woods because they enjoy adventuring, did the neighborhood kids dare them to go in, were they maybe chasing something that ran into the woods and led them to the portal? Something else?
Was the kid basically just chosen at random and for no important reason by whatever forces took them away? Does the kid miss their old life and just want to go home, do they embrace seeing this new world with open arms, are they just afraid and desperately trying not to get hurt or killed, or do they move between these perspectives, or feel bits and pieces of them simultaneously? What were they doing in the last 12 hours before they got whisked away?
Also... think through what you, when you were a child yourself, or some other kids you know or remember well from your own childhood would have done in your protagonist's position. Kids are people, too, with inner lives just as rich as those of adults.
"Jack, you have debauched my sloth."
Or: making The Generic Guy less generic.
For ages, I've been working on an Affectionate Parody of the "child has adventures with friendly magical being" genre of children's lit (Think The BFG, The Cat in the Hat, Mary Poppins, etc). The joke is that the magical being in question is an overeager dope who's terrible with children and doesn't realize he's endangering and generally scaring the shit out of them.
My problem is the child character. I can't seem to make one that's interesting enough. I've tried boys and girls, Bart Simpsons and Morty Smiths, but they all end up being reactive, kinda generic characters with very little going on under the hood. I want this character to be at least somewhat entertaining to "watch" even if the magical friend weren't there. Can someone out there give me some tips?
Is that a Wocket in your pocket, or are you just happy to see me?