Charlie's our hero, but he's not our narrator. Our narrator is someone else entirely, who has the ability to know and see a lot of things our Charlie couldn't, like in Chapter 10, when Grandpa Joe worries about Charlie to his wife (10.10). But what really matters here is that even though our narrator is a stranger, we get to dip into Charlie's head. A lot.
There's another passage in Chapter 10 that's worth checking out. It's a moment when we get to experience the world through Charlie:
Part of it was buried under the snow, but he saw at once what it was.
It was a fifty-pence piece!
Quickly he looked around him.