Jennings feels trapped in isolation throughout the book. He is isolated from his family by age and by decision, because his family are all alcoholics. His mother is so incompetent she just straight-up abandons him, lying to him and saying she'll be right back, but never coming back, only to show back up years and years later to make amends. But she is still so incompetent that she cannot even protect her own self from her clumsiness and drunkenness. Does that mean Jennings hates her? Absolutely not, because at the end of the day, his decision to become an officer was a decision to treat his whole community as his real family.
The foster parents are interesting foils to the real parents. Consider the evil of the Burch parents, whose problems come from vices and serious mental health issues. Then, consider the Carpenters, a manipulative family who decides to adopt a child they do not want, just for the tax write-off, only to abuse the child and treat him as an animal, like the Cage from the title, no doubt. They are different failures, but at the end of the day, Jennings must find home and peace, and there is only so much he can gain by holding them accountable who won't hold themselves accountable.
Survival and escape are deeply engrained in Jennings life, and the horror of his life as a rejected, abandoned son were only mitigated by the friendships he has through the orphanages, which ebb and flow, but there is one girl in particular who matters both symbolically and literally: Stacy. Stacy represents the alternative love that Burch doesn't get from his mother. She represents a genuinely desirable girl who treats Jennings with friendliness and dignity, something he is unaccustomed to by his daily life.
