What are some themes in the memoir "The Glass Castle" ?

One of the most prominent discussions presented in the
book is the idea of parenting and how to do it.  Walls and her siblings were not brought
up in a home that displayed "traditional" parent-child relationships and arguably, much
of what they endured as children could be considered abuse or neglect.  However, one
idea explored through this is the question of whether Jeanette turned out "normal"
despite her upbringing.  Many would argue that she did.  It seems, also, that she
defends both her parents love for herself and her brother and
sisters.

Another theme which somewhat results from the
above is the notion of family loyalty.  Consider the humorous and straightforward tone
of the book.  It is clear that though Walls is presenting memories with brutal honesty
and is well aware of how her childhood will appear to the rest of the world, she also
speaks with a defensive tone as if to say that she is the only one who is allowed to
judge her parents based on their parenting.  As a child, she is fiercely loyal
throughout the story to her entire family.

Finally, you
could explore the theme of poverty and survival.  The children in the Walls family are
nothing if not survivors.  Consider the many things they do to "fit in" in their
schools, to find food, and protect their odd parents from the judgemental eye of
others.  They are resilient, both physically and emotionally, and take care of
themselves and each other.