Those opening two lines are so impactful. And then you end both with a period, forcing the reader to dwell on them. Could they be joined into one sentence? Easily. But then the impact is lessened. And each is its own message. And the two combined add up to one even more.

"Thinly-worn smiles" is a good phrase. Worn-out smiles, and smiles just barely put in place. One obeys societal norms, but one often doesn't care to let the other know that is all they are doing. Reminds me when Americans start shooting the "Sir"s when their actual intent is to convey how little they think of the other person.
And "Second-hand treatment," as if you're used goods, something they got handed without wanting to take care of you. Which is sort of the case in your childhood, but the treatment and malice were all first-hand, first-grade, eh?

And then we get to the biggest motif of the piece, of the one waiting in the shadows. "Waiting in the shadows"? More like banished to the shadows, and then watching from them, wary of human contact, just beyond firelight, her eyes glow in the dark. She is what the children are warned of, the witch in the woods. But why does she live in the woods? And why is she supposed to be full of rancor and resentment? Because she was pushed to the woods. And we are always afraid of retribution we deserve. So we try to make sure it will never come back.

Are the wolves exiled? Or did they leave of their own accord, not wishing to be near those rowdy humans?
But a human is not a wolf. While wolves can make do with their own company, a human still must find love from other humans. Humans that resent him or her, and that they might resent in turn.
Because resentment breeds resentment.

And that brings us to the end of the piece, the last two stanzas.
A child always knows.
And an adult never forgets.

And people, more than they are people, are memories. And memories are ghosts that haunt us, that walk with us as we walk through life. Through life's shadowed hallways.