The theme appears reasonable. There are issues regarding domestic violence, a drunken father killing the mother, police protection, orphanage and foster homes. The girl gets a family and protective foster brothers.
I think the gaps will be filled in as the novel expands into several chapters. Questions like what happened to her real father? did the police file a case against him or not, etc. spring up.
Of course details like the bonding between Sam and her new-found brothers and the rest of the family, and the other three children who were friends with them have to inserted to complete the story.
Dialog and setting need to be put in place.
I think as you work on with the details, you will find new angles and perspectives that lend flesh and blood to the novel.

Write on!