It's a sad world, but understand to end up in the foster care system means no grandparents or siblings of the parents willing to step forward. Nor do the parents have any friends who are willing to step forward. Foster care is the last resort.
But the results coming out of foster care are all over the place. I know a physician who is out of foster care. He got lucky in high school and one of the science teachers he had really worked with him. I had several kids in foster care who ended up in state prison.
I had one female, who both the case worker and I thought would make it. Went to UNH, was on the Dean's List, and doing good. Then she had a touch of the stupids when she was 20, engaged in criminally reckless behavior, and that was that. Nice girl, not really criminal, just some stupid behavior that most teens are capable of, and some bad luck and no safety net.
But done right, an author can make their foster child into anything they want. Because it does happen. They need to make a connection with an adult, and the adult has to have the ability to hang in there. The kid will have problems with appropriate relationships, especially in the area of sexual relationships. Substance abuse is likely to be a concern. (The MD I know avoids all alcohol -- he looked at his family history and rejected the whole idea.) Mental health issues are the norm.
One of the things that is so depressing is you put a kid in a new school. Fresh start. Yeah, they find all the losers in the new school and it's back to the status quo. But that's who they're comfortable with.
Best of luck,
Jim Clark-Dawe