I get what they're saying, particularly about shoving a kid into that kind of situation. But it's a hypothetical at this point, so it's kinda pointless.
But, if anyone gives a shit, lemme give my opinion about "color" changes of characters in a visual medium from a written one.
It is only rarely a problem. There are stories that can't be divorced from ethnicity, and thus race/color. Same with culture. But mostof what gets complained about is stories where it just doesn't matter.
There's no main character in the potterverse that couldn't be another skin color, period. Even the Weasleys could be black or whatever. It wouldn't change anything about how they exist within the wizarding world. Even the side characters, the only reason it would matter is that some of them would be a little weird; Cho Chang being caucasian just seems like a pointless thing if that's the only change made.
But, even then, if you're just hiring the best actors for a role, and completely ignoring ethnicity, it doesn't matter. None of the characters being a different ethnicity would matter unless you changed them to muggles or squibs. You also couldn't change their nationality to anything but British without having to explain it since Hogwarts is supposedly just for British wizards, but you could change it and give an explanation and it wouldn't change the story.
So, let me illustrate this with the reason I mentioned being an author.
My current series is about a guy that's of Irish descent. I picked that because where he lives in the story was physically connected to the west coast of England and Ireland millions and millions of years ago. There's worldbuilding in there where him being of Irish descent is useful. The secondary character is African American, and that was because of both other worldbuilding choices and because I wanted a character that matched my friends and neighbors, some of whom are African Americans.
But you could switch their ethnicities and it wouldn't matter. The only thing that would have to change is why the main character and his family, being black, were able to settle in that section of the Appalachians back before the trail of tears happened, without eventually running into major hassles just for being free black people.
That's background though.
The connection is that both series (Potter and mine) are set in fictional worlds with fictional characters. It's all imaginary. This isn't history books we're talking about, we aren't upending things by shifting around skin colors. They just don't matter because you can change the off-screen worldbuilding and make it fit.
Now, the real hot take?
You could make a movie about George Washington, and cast Ildris Elba in the role, and it still wouldn't matter. The actor being black only matters if you refuse to recognize that acting is all playing pretend.
Is it harder to suspend disbelief when an actor doesn't visually come close to a historical figure? Hell yes it is. But it ain't like Idris Elba would be much more of a stretch than Joe Pesci. Think about it for a second. Which one could you picture being a general leading a rebel army? Which one would look better standing at the front of a boat crossing the Potomac?
I'm not knocking Pesci. Dude can act. But he visually matches the role of Washington less than Ildris Elba. But neither of them match the person George Washington at all, visually. Ildris being black is no more or less crazy than Joe being Italian, as actors portraying Washington.
It only matters what the actor of a role looks like because we place too much weight on the matter. When it comes right down to it, Washington having to be played by a white dude of English ancestry (iirc, ol Georgie might have had other stuff in the mix) is just because people can't be bothered to suspend disbelief when there's something that goes against their preconceptions.
Not that it would be easy for me to suspend disbelief and sink into a movie about Washington, when Uma Thurman is playing the role. But IF you put her in a silly hat and put her on a horse, does it really matter?
Now, you want something that matters? Try refilming Roots with Chinese actors. That's a massive mountain of disbelief to climb over. And it bypasses the story as a story of African people being stolen from Africa and enslaved. It could be done, but the story itself is so intrinsically tied to the black experience in america that trying to excise that part would make it almost impossible to immerse into, regardless of the ethical questions of negating black representation on screen.
And I chose Chinese for the example because there's a similarity there, where Chinese people came here and were abused for the profit of rich white people. So you could actually stretch the idea and make it a feasible choice. It would be a very bad idea, when you could just tell the story of the Chinese people's experience as workers instead, but it could be done.
The idea that an actor has to look as much like their role was in its original form is one of convenience, not necessity