Miles

Our first meeting with miles, is slightly different real note we hear of him is regarding his dismissal from the school:

"They absolutely decline."
"They go into no particulars. They simply express their regret that it should be impossible to keep him. That can have only one meaning." Mrs. Grose listened with dumb emotion; she forbore to ask me what this meaning might be; so that, presently, to put the thing with some coherence and with the mere aid of her presence to my own mind, I went on: "That he's an injury to the others."
At this, with one of the quick turns of simple folk, she suddenly flamed up. "Master Miles! HIM an injury?"
" Why, he's scarce ten years old."

With this conversation between Mrs. Grose and the governess, the reader gets two opposing sides of Miles.
The first is that he is a rather nasty child. They dismissed him, as in expelled. However, the gentlemen at the school went into no detail. So for what reasons he could be getting dismissed for that is still a mystery. However, the governess buts it as, "that he's an injury to the others." Though i dont know exactly what that might mean, it seems probable that it results from the idea of the student in class that is always a distraction. Especially in a school that is private, and for the upper class, any student that may pose as a "bad example" will probably not be tolerated for very long. So just based off this the reader's impression of Miles is not good, rather it seems that he is spoiled and obnoxious the opposite of what his sister is. It would seem like he has no manners and is being sent home because he can not behave himself.
The other view is that of Mrs. Grose's- first she is all disbelief. Its as if this could simply not be true because it is contradictory to his character. Then she invokes the idea of how young he is, to show that whatever the problem is its probably not his fault. She quickly displaces the blame from him onto the headmasters at the school. She later on invokes his appearance, demanding that the governess see him first and then judge him. But even if his appearance is angelic that shouldn't dictate what his actions maybe. With looking at Miles through Mrs. Grose's view, readers would get a very different sense one that is more consistent of a grandmother. That Miles is naturally sweet and just generally misunderstood. Like with Flora readers are too masked and uncertain at this point to be able to make any real assumptions about her.