Why does Cosette sing ''Castle On A Cloud''? Extra credit for music class

The song is sung by Little Cosette while dreaming of a better life instead of the life with the Thénardiers. She dreams of a "castle on a cloud", a realm of her own imagination where all children are free to play and she is loved. The third verse speaks of a lady all in white who loves her and it is implied that this is her vision of her mother, Fantine. Madame Thénardier intervenes during the song and verbally abuses Cosette, ordering to "draw some water from the well in the wood", despite the fact that it is cold outside and Cosette is afraid. Meanwhile, Madame Thénardier dotes on her own young daughter Éponine.

Because they wanted to