Yes. The child and the sky were aching blue. ??
Okay, He dreamt of walking in a flowering wood where birds flew.
Don't we need some punctuation here? Does "before them" go with "flew," or with "he and the child"?
"Where birds flew before them," or "Before them, he and the child and the sky were aching blue."
"But he was learning how to wake himself from just such siren worlds," stands perfectly well on its own.
The junction around the word "before" needs to be fixed. I don't know what you mean.