Putting on black face is just not a good idea. It may be "innocent" as the kid wanting to be a close representation of their favorite athlete, who may be black. But, Black Face use in the past has such a negative and racist connotation, it's just a bad idea.
But, using as a true dress up isn't blackface, it's an actual costume/makeup. Sometimes making things normalized help get rid of past transgressions of people. Make it so when somebody sees it they don't even think of blackface, they just think and see a costume.
I get what you are saying CN, so if someone was trying to portray another person from another race, a mask would be a better choice. I just think that any time a white person puts on makeup to make themselves look like another race, it's just a bad idea, and offensive to the other race. It's not exactly black-face, but its closer to being black-face than not black-face. I am white, so I am assuming that it would be offensive to the black/Hispanic/Asian/etc. person.
I think it would be weird, but I don't think I would be offended by it. Dave Chapelle has put white make-up on on his old TV show to act like a white guy, and I thought it was hilarious. But, I don't get easily offended by things.
I am not an expert on racism or race relations, but I think the main reason that Black/Asian/Hispanics can make themselves look white, is because they never had the "power" over the white people which creates racism. So, when white people go to make themselves look like another race, it's a form of exerting the past, racist power over them.
Again, there are just certain things that aren't a good idea in today's world. A white person doing something to make themselves look like another race, even if it were a "tribute" isn't a good idea.
I can understand why people don't understand it when they're dressing as a specific person, like Lebron James.
The (historical) problem is people dressed up as a "typical" Black person before. Then acted like they perceived Black people to act. Like they would dress up as a clown or a witch or a ghost.
So it might not necessarily be wrong to try to look as close to Lebron James as you can but it's also understandable for people to be upset by it. And those same people probably aren't dressing in White face.
I don't think it makes Megyn Kelly a racist to ask those questions. But I do think not having the wherewithal to not ask it on TV is a fireable offense.